Hydrokinetic torque converter and lockup clutch therefor

ABSTRACT

A hydrokinetic torque converter is provided with a lockup clutch wherein the piston and other constituents of the lockup clutch are adequately cooled during each stage of operation of the torque converter and its clutch. The piston of the lockup clutch and/or the component which cooperates with the piston to transmit torque from the housing directly to the turbine of the torque converter is provided with a friction lining which establishes a portion of the path for the flow of fluid coolant between the fluid-filled compartments at opposite sides of the piston. The rate of fluid flow between the compartments is regulated by one or more adjustable valves which are carried by the housing of the torque converter and/or by the piston of the lockup clutch.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/545,452, filed Apr. 7, 2000, which is a divisional of U.S.patent application Ser. No. 08/978,389, filed Nov. 25, 1997 (now U.S.Pat. No. 6,062,358), which is a divisional of U.S. patent applicationSer. No. 08/272,920, filed Jul. 8, 1994 (now abandoned); all of whichare incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] The invention relates to improvements in hydrokinetic torqueconverters and to improvements in lockup clutches or bypass clutches foruse in torque converters. More particularly, the invention relates toimprovements in torque converters of the type wherein a rotary housingis provided with a chamber for a pump, a turbine, a stator and lockupclutch having an axially movable annular piston which divides thechamber into a first compartment and a second compartment. The chamberis filled with a suitable fluid (such as oil), and the piston of thelockup clutch carries a first friction surface which can be moved intotorque transmitting contact with a second friction surface when the slipclutch is engaged. Still more particularly, the invention relates toimprovements in hydrokinetic torque converters and lockup clutcheswherein the first compartment is disposed between the piston and acomponent which carries the second friction surface, and wherein thepiston and/or the aforementioned component is provided with one or morepassages to establish a path for the flow of fluid from the secondcompartment substantially radially inwardly toward the rotational axisof the housing.

[0003] European Pat. No. 0 078 651 discloses a torque converter having alockup clutch which includes an annular piston. That side of the pistonwhich faces away from the friction surfaces is provided with channelsserving to establish paths for the flow of fluid between a firstcompartment which is bound by a radial wall of the housing and thepiston, and the second compartment which confines the pump and theturbine of the torque converter. The direction of fluid flow is from thesecond compartment into the first compartment so that the fluid can coola viscous coupling which transmits torque between the piston and the hubof the turbine.

[0004] U.S. Pat. No. 4,969,543 (granted Nov. 13, 1990 to Macdonald for“Slipping Bypass Clutch Construction for a Hydrokinetic TorqueConverter”) discloses a lockup clutch having an annular piston providedwith a first friction surface movable against a second friction surfaceprovided on a radially extending wall of the housing. The piston or thefriction lining on the wall of the housing is provided with channelswhich permit a fluid to flow from the second compartment into the firstcompartment within the housing even when the lockup clutch is engaged.The channels are provided at the same radial distance from therotational axis of the housing as the friction surfaces, the firstcompartment is disposed between the piston and the wall of the housing,and the second compartment accommodates at least the turbine of thetorque converter. In the patent the patentee desires to preventexcessive thermal stressing of certain parts of the torque convertersuch as could develop during continuous slipping of the frictionsurfaces during operation of the converter. More specifically, thepatentee desires to prevent excessive thermal stressing of parts in theregion of the two friction surfaces.

[0005] Published Japanese patent application No. 58-30532 also disclosesa lockup clutch or bypass clutch which is intended for use in ahydrokinetic torque converter and is provided with channels in theregion of its friction surfaces.

[0006] The aforementioned patent to Macdonald is but one of numerouspublications which propose the utilization of a lockup clutch whosefriction surfaces slide relative to each other in the disengaged as wellas in the engaged condition of the clutch. If the torque converter isinstalled in the power train of a motor vehicle, the slippage of thefriction surfaces forming part of the lockup clutch can be short-lasting(e.g., during shifting into a different gear) or such slippage can bemaintained practically within the entire operating range of the torqueconverter. The extent and the duration of slippage can depend upon thedesign of the prime mover which drives the housing of the torqueconverter and/or upon the selected gear ratio and/or upon one or morevariable parameters of the prime mover. The lockup clutch dissipatesenergy in the form of heat during slippage of its friction surfacesrelative to each other, and the quantity of dissipated energy can bequite pronounced (e.g., in the range of several kilowatts) duringcertain stages of operation of the torque converter. Such a situationcan develop, for example, when a vehicle pulling a trailer is drivenalong a mountain road, i.e., the torque converter is apt to dissipatelarge amounts of energy for an extended period of time. Moreover, whenthe slip clutch is engaged, the amount of dissipated energy can begreatly increased, at least for a short interval of time, i.e., thetorque converter and its lockup clutch are apt to be heated well above apermissible maximum temperature.

[0007] The purpose of the establishment of one or more paths for theflow of a fluid coolant is to prevent the aforediscussed drawbacks ofheretofore known torque converters and their lockup clutches. A drawbackof heretofore known proposals to cool the lockup clutch of a torqueconverter is that the maximum torque which the lockup clutch cantransmit is insufficient, and this is attributable to certain dynamic orkinetic conditions which develop in the fluid flow. The ability ofconventional lockup clutches to transmit torque decreases in response toan increasing RPM of the housing of the torque converter as well as inresponse to increasing rate of fluid flow. This means that, if only thelockup clutch of a heretofore known torque converter is to transmittorque when the RPM of the housing rises to a preselected value, it isnecessary to increase the system pressure accordingly. This, in turn,renders it necessary to employ stronger parts, such as a stronger andbulkier piston as well as a higher-capacity pump. Furthermore, the rateof fluid flow per unit of time is then increased again which results inadditional losses.

[0008] The aforementioned reduction of the ability of the lockupclutches in conventional torque converters to transmit torque isattributable, among other causes, to the development of forces generatedas a result of certain dynamic conditions acting upon the radiallyinwardly flowing fluid in a sense to increase the fluid pressure. Suchforces generate a component acting in the direction of the rotationalaxis of the housing of the torque converter so that the piston is urgedto move in a sense to disengage the lockup clutch.

[0009] A further drawback of heretofore known undertakings to cool thetorque converter in the region of the lockup clutch is that the flow ofcooling fluid is overly dependent upon the temperature and/or viscosityof the fluid (such as oil) and/or the difference between fluid pressuresat opposite sides of the piston. This means that, if a torque converterand its lockup clutch are constructed and assembled in a manner asproposed, for example, in the aforementioned patent to Macdonald, theresistance to the flow of fluid in the channels between the twofluid-containing compartments must be selected to be satisfactory evenunder critical circumstances, i.e., the rate of flow of fluid whosetemperature has risen to a maximum possible or permissible value is lessthan the rate at which the system pressure in the torque converter woulddrop or collapse to an unacceptably low value. In the patented torqueconverter of Macdonald, the rate of fluid flow in the channels betweenthe two compartments at opposite sides of the piston of the lockupclutch is directly dependent upon the difference between the fluidpressures in the two compartments. Such pressure differential is thevariable parameter which controls the transmission of torque by thelockup clutch and, therefore, it cannot be resorted to for the selectionof the desired volumetric flow of the fluid. Thus, and in order tomaintain the losses in the torque converter above a minimum acceptablevalue, the rate of fluid flow must be low even when the differencebetween the fluid pressures in the two compartments rises to a maximumvalue, i.e., when the converter is called upon to transmit a maximaltorque. This may ensure a satisfactory rate of the flow of fluid coolantwhen the converter is called upon to transmit maximum torque but isunsatisfactory during transmission of lesser torque because thedifference between the fluid pressures in the two compartments of thetorque converter is too low.

OBJECTS OF THE INVENTION

[0010] An object of the present invention is to provide a novel andimproved torque converter which is capable of transmitting largetorques.

[0011] Another object of the invention is to provide a hydrokinetictorque converter which can transmit large torques without risking anoverheating of its constituents.

[0012] A further object of the invention is to provide a conveyancewherein the power train embodies the improved hydrokinetic torqueconverter.

[0013] Still another object of the invention is to provide a torqueconverter with a lockup clutch or bypass clutch which is constructed andassembled in such a way that it is adequately cooled in the region ofits friction surfaces.

[0014] A further object of the invention is to provide a torqueconverter wherein the fluid is not overheated irrespective of theprevailing conditions.

[0015] Another object of the invention is to provide a hydrokinetictorque converter wherein the rate of fluid flow in the region of thelockup clutch is not only acceptable but rather highly satisfactoryirrespective of the circumstances of use of the torque converter and itslockup clutch.

[0016] An additional object of the invention is to enhance the exchangeof heat between the parts of the lockup clutch in a hydrokinetic torqueconverter and a fluid coolant.

[0017] Still another object of the invention is to provide a lockupclutch or bypass clutch which is installed in a hydrokinetic torqueconverter and is constructed and assembled in such a way that themagnitude of torque which the clutch is to transmit can be selected andvaried with utmost precision. A further object of the invention is toprovide a lockup clutch or bypass clutch which can be utilized in ahydrokinetic torque converter and is constructed and assembled in such away that the extent of slippage between its friction surfaces can beregulated with a heretofore unknown degree of precision.

[0018] Another object of the invention is to provide a lockup clutchwhich can be installed in the housing of a hydrokinetic torque converterand wherein the slippage between the friction surfaces can be selectedwith a view to satisfactorily compensating for surges and/or otherirregularities of torque transmission regardless of whether theirregularities are attributable to the prime mover which drives thehousing of the torque converter and/or to the power train between theprime mover and the housing.

[0019] An additional object of the invention is to enhance the comfortof the occupant or occupants of a motor vehicle wherein the power trainbetween the prime mover and the wheels embodies a hydrokinetic torqueconverter and a lockup clutch or bypass clutch of the above-outlinedcharacter.

[0020] Still another object of the invention is to provide a novel andimproved means for regulating the rate of fluid flow betweencompartments at opposite sides of the piston in a lockup clutch which isembodied in a hydrokinetic torque transmission.

[0021] A further object of the invention is to provide novel andimproved piston or pressure plate for use in a lockup clutch of theabove-outlined character.

[0022] Another object of the invention is to provide novel and improvedfriction linings for use in the lockup clutches of hydrokinetic torqueconverters.

[0023] An additional object of the invention is to provide a novel andimproved housing for use in a hydrokinetic torque converter.

[0024] Still another object of the invention is to provide a novel andimproved lockup clutch or bypass clutch which can be utilized in ahydrokinetic torque converter and whose operation can be regulated toconform to one or more variable parameters of the torque converter, ofthe means for driving the torque converter and/or of means receivingtorque from the torque converter.

[0025] A further object of the invention is to provide a simple, compactand inexpensive torque converter and a simple, compact and inexpensivelockup clutch or bypass clutch for use in such torque converter.

[0026] Another object of the invention is to provide a novel andimproved method of establishing, dimensioning and orienting fluid flowpermitting passages and/or channels in the regions of the frictionsurfaces in a lockup clutch or bypass clutch for use in hydrokinetictorque converters.

[0027] An additional object of the invention is to provide a lockupclutch which can be utilized in the above-outlined novel and improvedhydrokinetic torque converter and even in certain types of conventionaltorque converters.

[0028] Still another object of the invention is to provide a lockupclutch wherein the piston or pressure plate can perform one or moreimportant functions in addition to that of engaging and disengaging theclutch.

SUMMARY OF THE INVENTION

[0029] One feature of the present invention resides in the provision ofa hydrokinetic torque converter which comprises a housing which isrotatable about a predetermined axis and is provided with afluid-containing chamber for the pump, turbine and stator of the torqueconverter. The latter further comprises a novel and improved engageableand disengageable lockup clutch or bypass clutch which is interposedbetween the housing and the turbine and comprises an annular pistonmovable in the chamber in the direction of the predetermined axis anddividing the chamber into a first compartment which is disposed at afirst radial distance from the axis and a second compartment. The lockupor bypass clutch (hereinafter called lockup clutch or clutch for short)comprises a first friction surface which is (directly or indirectly)carried by the piston at a second radial distance from the axis greaterthan the first radial distance and a second friction surface carried bya component which is rotatable with the housing. The first frictionsurface confronts and is in contact with the second friction surface inthe engaged condition of the clutch, and the piston and/or the componenthas at least one passage for the flow of fluid from the secondcompartment substantially radially inwardly toward the firstcompartment. The clutch further comprises first and second members whichdefine at least one channel serving to establish a path for the flow offluid from the at least one passage into the first compartment andwherein the fluid acts upon the first and/or the second member in thedirection of the predetermined axis. Still further, the clutch comprisesmeans for preventing axial movements of the piston in the direction ofthe predetermined axis in response to the action of the fluid in the atleast one channel. Otherwise stated, the first and second members arepropped or held relative to each other in the direction of thepredetermined axis in such a way that the power flow between them is anendless (closed in itself) flow.

[0030] The piston of the lockup clutch is preferably provided with atleast one friction lining and the first friction surface is thenprovided on the at least one friction lining. Furthermore, the first orsecond member can form part of the piston, i.e., the piston can definethe at least one channel jointly with the second or first member.Otherwise stated, one of the first and second members can form part ofthe piston.

[0031] The orientation of the at least one passage can be such that itestablishes a path for the flow of fluid from the second compartmenttoward the first compartment.

[0032] The means for preventing axial movements of the piston in thedirection of the predetermined axis in response to the action of fluidin the at least one channel can include means for connecting the firstand second members to each other.

[0033] In accordance with a presently preferred embodiment, one of thefirst and second members bounds a portion of the first compartment andis affixed to the aforementioned component or to the piston, and the atleast one channel is then provided in the one member.

[0034] One of the first and second members can be rigid with (e.g.,riveted to or of one piece with) the piston or the component.

[0035] The component can include or constitute or form part of a wallwhich, in turn, forms part of the housing and extends substantiallyradially of the predetermined axis. The first compartment is disposedbetween the wall and the piston, as seen in the direction of thepredetermined axis.

[0036] The piston can be installed between a wall of the housing and theturbine of the torque converter.

[0037] If one of the first and second members forms part of the piston,the at least one channel can be provided in the piston.

[0038] It is also possible to mount the first or second member on thepiston, and the first or the second member can be disposed in the firstcompartment of the chamber in the housing of the torque converter.

[0039] The piston can be disposed in the housing between one of thefirst and second members and the first compartment.

[0040] The pump and the turbine of the torque converter are installed inthe second compartment. One of the first and second members can dividethe first compartment into two sections which are adjacent each other asseen in the direction of the predetermined axis.

[0041] At least one friction lining can be provided on theaforementioned component and/or on the piston. The at least one passageis then adjacent the friction lining, and such passage can be providedin the friction lining.

[0042] The inlet of the at least one passage can be disposed at a firstradial distance from the predetermined axis, and the outlet of suchpassage can be disposed at a lesser or shorter second radial distancefrom the axis.

[0043] The width of the first compartment (as measured radially of thepredetermined axis) can be selected in such a way that its exceeds thelength of the at least one channel. It is presently preferred to selectthe ratio of the width of the first compartment to the length of the atleast one channel in such a way that the length of the channel is notless than 50% of the width of the first compartment.

[0044] The at least one passage can constitute a cutout in, or isstamped or embossed into, the friction lining on or of theaforementioned component and/or the piston.

[0045] The inlet of the at least one passage can extend substantiallyparallel with the predetermined axis, and such inlet can be provided inthe aforementioned component and/or in the piston. Furthermore, theoutlet of the at least one passage can extend substantially parallelwith the predetermined axis and can be provided in the piston and/or inthe aforementioned component.

[0046] The at least one passage in the friction lining on the componentand/or on the piston can be configurated in such a way that itestablishes a substantially meandering or zig-zag shaped path for theflow of fluid (e.g., oil) between the at least one channel and thesecond compartment.

[0047] If the piston is provided with at least one friction lininghaving a first portion disposed at a lesser first radial distance and asecond portion disposed at a greater second radial distance from thepredetermined axis, the at least one passage can be provided in the atleast one friction lining in such a way that it has an inlet at leastclose to one of the first and second portions of the at least onefriction lining and an outlet which is at least close to the other ofthe first and second portions of the at least one friction lining.

[0048] The at least one friction lining of the annular piston definesthe respective friction surface and can extend substantiallycircumferentially of the piston. The at least one passage can beprovided, at least in part, in the friction lining to extendsubstantially circumferentially of the piston and to define asubstantially meandering or zig-zag shaped path for the flow of fluidbetween the at least one channel and the second compartment.

[0049] If the at least one passage establishes a substantiallymeandering or zig-zag shaped path for the flow of fluid between thesecond compartment and the at least one channel, the configuration ofthe passage is or can be such that it includes at least two turns, i.e.,the fluid flowing therein is compelled to change the direction of flowmore than once.

[0050] As already mentioned above, the piston can comprise or carry atleast one friction lining, and the respective friction surface is thenprovided on such friction lining.

[0051] The friction lining of the aforementioned component or of thepiston is provided with the respective friction surface, and suchfriction lining can comprise or can be composed of at least two arcuatesections.

[0052] In accordance with another feature of the invention, the lockupclutch can further comprise means for regulating the flow of fluid inthe at least one passage as a function of variations of at least onevariable parameter of the torque converter. The arrangement can be suchthat the regulating means controls the flow of fluid in the at least onepassage in dependency upon variations of at least one variable parameterof the torque converter and/or as a function of at least one variableparameter of the means (e.g., a combustion engine in a motor vehicle)for driving the housing of the torque converter and/or as a function ofat least one variable parameter of the means for receiving torque fromthe turbine of the torque converter. For example, the torque convertercan transmit torque to an automatic transmission in a motor vehicle.

[0053] The means for regulating the flow of fluid in the at least onepassage can constitute or include an adjustable valve which is installedat the inlet or at the outlet of the at least one passage. Such passagecan be defined by a suitably shaped portion of the aforementionedcomponent and/or the piston. The component can constitute a wall, andthe at least one passage (or at least one of plural passages) can bedefined by a suitably shaped portion of such wall. For example, the atleast one passage can be provided in the annular piston, and at leastone additional passage can be provided in the piston or in theaforementioned component (such as a wall of the housing).

[0054] The valve or any other suitable fluid flow regulating means canbe designed in such a way that it includes means for regulating the flowof fluid through the at least one passage to ensure that the rate offluid flow through the passage is at least substantially constant withinthe entire operating range of the torque converter.

[0055] The pressure of fluid in the first compartment can differ ordiffers from the fluid pressure in the second compartment during atleast one stage of operation of the torque converter, for example, whensuch torque converter is installed in the power train of a motorvehicle. The aforementioned valve or equivalent means for regulating theflow of fluid in the at least one passage is then designed to regulatethe fluid flow as a function of differences between the fluid pressuresin the two compartments. The valve is designed to reduce the rate offluid flow in the at least one passage in response to increasingdifferences between the fluid pressures in the two compartments.

[0056] If the valve is acted upon by centrifugal force in response torotation of the aforementioned component and/or the piston, it ispreferably provided with (or the lockup clutch further comprises) meansfor varying the rate of fluid flow in the at least one passage as afunction of changes of differences between fluid pressures in the firstand second compartments and at least substantially independently of theaction of centrifugal force.

[0057] It has been found that the rate of fluid flow in the at least onepassage is quite satisfactory if such rate is different from the squareroot of the difference between fluid pressures in the first and secondcompartments.

[0058] Another feature of the invention resides in the provision of ahydrokinetic torque converter which comprises (1) a housing having afluid-containing chamber which is rotatable about a predetermined axis,(2) a pump, (3) a turbine and a stator in the chamber, and (4) anengageable and disengageable lockup clutch which is interposed betweenthe housing and the turbine. The clutch comprises an annular pistonmovable in the chamber in the direction of the predetermined axis anddividing the chamber into a first compartment and a second compartment.The clutch further comprises a first friction surface which is providedon at least one friction lining of the annular piston, and a secondfriction surface carried by a component which is rotatable with thehousing and serves to confront and contact the first friction surface inthe engaged condition of the clutch. The friction surfaces are disposedat a first radial distance from the predetermined axis, and the firstcompartment is disposed at a lesser second radial distance from suchaxis. The piston and/or the component is provided with at least onepassage for the flow of fluid from the second compartment toward thefirst compartment in the engaged condition of the clutch, and suchpassage is disposed at the aforementioned first radial distance from thepredetermined axis. The clutch further comprises a wall which isdisposed in the first compartment and extends substantially radially ofthe predetermined axis to define with a second wall at least one channelwhich establishes a path for the flow of fluid from the at least onepassage into the first compartment, and means for connecting the wallsto each other against movement relative to one another in the directionof the predetermined axis. The second wall preferably extends at leastsubstantially radially of the predetermined axis.

[0059] The second wall can form part of the piston, and the clutch canfurther comprise means for connecting the first wall to the housingagainst movement relative to the housing in the direction of thepredetermined axis. Still further, the torque converter or its clutchcan comprise means for connecting the first wall to the hub of theturbine so that the first wall is held against movement relative to theturbine in the direction of the predetermined axis.

[0060] Still another feature of the invention resides in the provisionof a novel and improved lockup clutch for use in a hydrokinetic torqueconverter and comprising a friction lining having at least one frictionsurface and at least one passage for the flow of a fluid coolant (e.g.,oil). The at least one passage is disposed at the at least one frictionsurface. The ratio of the thickness of the friction lining to theaverage depth of the at least one passage can be between 1.3 and 2.7.The depth of the at least one passage can be in the range between 0.2and 0.8 mm, preferably between 0.3 and 0.6 mm.

[0061] If the torque converter which embodies the improved lockup clutchis installed in a motor vehicle, the fluid coolant is or can be heatedwhen the vehicle is in actual use, and the at least one passage is orcan be configurated in such a way that it ensures the developement of aturbulent coolant flow at its inlet and/or at its outlet when thevehicle is in actual use.

[0062] The at least one passage of the improved lockup clutch can extendin the circumferential direction of an annular piston which forms partof the clutch and carries the friction lining. The at least one passagecan establish for the fluid coolant a path which is an at leastsubstantially meandering or zig-zag shaped path, and the at least onepassage can have an at least substantially constant cross-sectionaloutline between its inlet and its outlet. The friction lining whichdefines a substantially meandering or zig-zag shaped path can have asubstantially circular shape.

[0063] If the improved clutch is embodied in a torque converter havingat least one variable operational parameter and being driven by a primemover (e.g., a combustion engine having one or move variable parameters)to transmit torque to an automatic transmission or another torquereceiving unit having one or more variable parameters, the clutch can befurther provided with means (e.g., one or more valves or flowrestrictors) for regulating the flow of fluid coolant in the at leastone passage as a function of variations of at least one of theaforementioned parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved torque converter itself, however, both as to its constructionand its mode of operation, together with additional features andadvantages thereof, will be best understood upon review of the followingdetailed description of certain presently preferred specific embodimentswith reference to the accompanying drawings, wherein:

[0065]FIG. 1 is a fragmentary axial sectional view of a hydrokinetictorque converter and of a lockup clutch which embody one form of thepresent invention;

[0066]FIG. 2 is a diagram wherein the curves are characteristic oftorque transmission by certain conventional lockup clutches as well bythe improved lockup clutch;

[0067]FIG. 3 is a fragmentary axial sectional view of a modified torqueconverter and of a modified lockup clutch;

[0068]FIG. 4 is a fragmentary axial sectional view of a third torqueconverter and a third lockup clutch;

[0069]FIG. 5 is a fragmentary axial sectional view of a fourthhydrokinetic torque converter and a fourth lockup clutch;

[0070]FIG. 6 is an elevational view of a friction lining which can beutilized in the improved lockup clutch;

[0071]FIG. 7 illustrates three arcuate sections of a modified frictionlining;

[0072]FIG. 8 is a fragmentary axial sectional view of a furtherhydrokinetic torque converter and its lockup clutch;

[0073]FIG. 8a is a fragmentary axial sectional view of still anothertorque converter and of its lockup clutch which is provided with meansfor regulating the rate of fluid flow between the fluid-containingcompartments at the opposite sides of the piston or pressure plate;

[0074]FIG. 9 is an enlarged axial sectional view of the fluid flowregulating means of the lockup clutch shown in FIG. 8a;

[0075]FIG. 9a is an axial sectional view of modified fluid flowregulating means;

[0076]FIG. 10 is a fragmentary axial sectional view of a torqueconverter and a lockup clutch which is provided with differentlypositioned fluid flow regulating means;

[0077]FIG. 11 is a fragmentary axial sectional view of still anotherhydrokinetic torque converter and its lockup clutch; and

[0078]FIG. 12 is a fragmentary elevational view of a friction liningconstituting a modification of the friction linings shown in FIGS. 6 and7.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0079]FIG. 1 shows a portion of an apparatus 1 which can be utilized forthe transmission of torque from a prime mover (e.g. the internalcombustion engine of a motor vehicle) to one or more driven units, e.g.,to the differential for the wheels of a motor vehicle. The apparatus 1comprises a torque converter 3 having a housing 2 which defines achamber for a pump 7, a turbine 10, a stator 12 and a lockup clutch 15.The torque converter 3 forms part of the power train and can beinstalled and assembled with other constituents of the power train in amanner as disclosed, for example, in FIG. 1 of U.S. Pat. No. 4,993,406granted Jan. 15, 1985 to Bopp for “Viscous Bypass Coupling For TorqueConverter”. The disclosure of the patent to Bopp is incorporated hereinby reference.

[0080] The housing 2 of the torque converter 3 comprises two annularportions or sections 4 and 5 which are sealingly secured to each otherby a welded seam 6. Such seam is provided between the radially outermostpart of the housing section 5 and an axially extending cylindrical part4 a of the section 4. The section 4 can receive torque from a rotaryinput element I of the prime mover, e.g., the camshaft or the crankshaftof a combustion engine. FIG. 1 shows that the radially inner part of asubstantially radially extending wall 9 of the housing section 4 isdirectly connected to the output element I; however, it is equallypossible to employ an intermediate part, e.g., a washer-like sheet metalconnector which is interposed and transmits torque between the outputelement I and the housing section 4. The radially inner portion of suchconnector is affixed to the output element I and the radially outerportion of the connector is affixed to the section 4 of the housing 2.Reference may be had, for example, to the aforementioned publishedJapanese patent application No. 58-30532.

[0081] The section or portion 5 of the housing 2 which is shown in FIG.1 performs the additional function of constituting the casing or shellof the pump 7. The vanes or blades 8 of the pump 7 are affixed directlyto the section 5. The turbine 10 is installed in the chamber of thehousing 2 between the pump 7 and the substantially radially extendingwall 9 of the housing section 4. The radially inner portion of theturbine 10 is non-rotatably affixed to or is of one piece with a tubularhub 11. This hub is provided with axially parallel internal splineswhich alternate with teeth and can receive the complementary teeth atthe exterior of the rotary input element of a unit which is to receivetorque from the torque converter 3. For example, the hub 11 can transmittorque to the rotary input shaft of a gear ratio box as shown in FIG. 1of the aforementioned patent to Bopp.

[0082] The stator 12 of the torque converter 3 is installed in thechamber of the housing 2 between the radially inner portions of the pump7 and turbine 10. The radially inner portion of the housing section 5 isconnected to or provided with a sleeve-like hub 13 which can berotatably mounted in the case of a transmission.

[0083] The aforementioned internal chamber of the housing 2 is shown at14. The left-hand portion of this chamber receives the lockup clutch 15which, when engaged, can transmit torque directly between the housingsection 4 and the hub 11 of the turbine 10. The lockup clutch 15 isdesigned and mounted in such a way that it operates in parallel with thetorque converter 3. The chamber 14 further accommodates a damper 16which operates in series with the torque converter 3 and can include aset of arcuate coil springs or other suitable energy storing elementswhich can transmit torque from the annular piston or pressure plate 17of the lockup clutch 15 directly to the hub 11 of the turbine 10 whenthe lockup clutch is engaged. Reference may be had, for example, to U.S.Pat. No. 5,156,249 (granted Oct. 20, 1992 to Friedmann for “TorqueTransmitting Apparatus With Axially Deformable Primary Flywheel”) whichis assigned to the owner of the assignee of the present application.

[0084] The piston or pressure plate 17 (hereinafter called piston orannular piston) is installed in the chamber 14 at the wall 9 of thehousing section 4, and the radially inner portion of this piston haslimited freedom of movement relative to the hub 11 of the turbine 10 inthe directions of the axis 27 of the housing 2. The piston 17 dividesthe chamber 14 into a first compartment 18 adjacent the wall 9 and asecond compartment 20 which contains the pump 7, the turbine 10 and thestator 12. The compartment 18 is disposed radially inwardly of theregion 19 of frictional engagement of a friction surface on the piston17 (and more specifically of a friction surface on a friction lining 22forming part of the piston) with a friction surface 21 which is carriedby the housing section 4. The two friction surfaces are caused to abuteach other in the engaged condition of the lockup clutch 15.

[0085] The friction surface 21 of the housing section 4 is provided atthe inner side of a hollow frustoconical portion of the wall 9 radiallyoutwardly of the compartment 18, and the friction surface of thefriction lining 22 confronts the surface 21 in the engaged anddisengaged conditions of the lockup clutch 15. The two friction surfacestaper toward the axis 27 of the housing 2 in a direction away from thecompartment 20 and the parts 7, 10 and 12 therein. The friction lining22 is bonded or otherwise reliably secured to a hollow frustoconicalpart 23 of a disc-shaped member 24 which can be made of metallic sheetmaterial and is riveted (as at 17 r) or otherwise reliably affixed tothe piston 17 so that the members 17, 24 are held against axial movementrelative to one another. The piston 17 is or can be obtained bydeforming a suitable sheet metal blank, e.g., in a deep drawing machine.

[0086] Recently developed torque converters are designed in such a waythat the friction surfaces of their lockup clutches can slip relative toone another in the disengaged as well as in the engaged conditions ofthe lockup clutches. This applies in particular for torque converterswhich are installed in the power trains of motor vehicles. As alreadydiscussed hereinbefore, the ability of the friction surfaces of a lockupclutch to slip relative to one another in the engaged condition of theclutch (or at least during certain stages of operation of the motorvehicle) results in the generation of heat (i.e., dissipation of energy)which can be quite pronounced (e.g., in the range of several kilowatts).As also mentioned above, such situation can develop when a motor vehicleis coupled to a trailer and is driven along a mountain road. Stillfurther, the lockup clutch is likely to cause the torque converter togenerate large amounts of heat during engagement or disengagement of thelockup clutch. In addition to the aforediscussed patent to Macdonald,reference may also be had to German patent applications Nos. P 42 28137.7 and P 42 35 070.0-12 which also disclose torque converters withlockup clutches wherein the friction surfaces can slip relative to oneanother in the engaged condition of the clutch.

[0087] Excessive heating of the lockup clutch 15 could result in damageto or destruction of the friction lining 22 and would also adverselyaffect at least a substantial part of the supply of fluid in the chamber14 of the housing 2. In order to avoid excessive heating of fluid and ofvarious parts of the torque converter 3 and its lockup clutch 15 in theregion (19) of the friction surface 21 and the friction surface of thefriction lining 22, the lining 22 is provided with one or more suitablyconfigurated and dimensioned passages 25 for the flow of fluid from thecompartment 20 radially toward the axis 27 of the housing 2, i.e.,radially inwardly toward the compartment 18 between the member 24 on thepiston 17 and the wall 9 of the housing section 4. The passage orpassages 25 (hereinafter referred to in plural) permit the establishmentof an uninterrupted flow of fluid coolant across the region 19 betweenthe friction lining 22 and the friction surface 21, even when the lockupclutch 15 is engaged or practically engaged. The rate of fluid flow inthe passages 25 of the friction lining 22 along the friction surface 21is sufficient to ensure the withdrawal of substantial quantities of heatfrom the housing section 4, from the piston 17 and from the member 24.

[0088] One presently preferred form of the passages in the frictionlining of a lockup clutch which embodies the present invention will bedescribed with reference to FIGS. 6 and 7.

[0089] Each channel 25 has a inlets 26, 26 a which are provided in theradially outer portion of the disc-shape member 24 and through thepiston 17, respectively. The inlets 26, 26 a are aligned substantiallyparallel with the axis 27 of the housing 2 to establish a path for theflow of fluid from the compartment 20 into the respective passage 25toward the compartment 18 a. Each inlet 26 a can constitute a bore orhole in the body of the piston 17 and each inlet 26 can be a hole in adisc-shaped member 24. The outlets of the passages 25 are located at theradially inner portion of the friction lining 22 and communicate withchannels 18 a which discharge fluid into the radially inner portion ofthe compartment 18.

[0090] The channels 18 a are defined by two members of the lockup clutch15, namely by the sheet metal disc-shaped member 24 and the adjacentradially inner portion of the piston 17. The path for the flow of fluidfrom the compartment 20 radially inwardly toward the compartment 18 isestablished in part by the passages 25 in the friction lining 22 and inpart by the channel or channels 18 a between the piston 17 and themember 24. Such path allows the fluid to flow from the compartment 20toward and into the compartment 18 irrespective of whether the lockupclutch 15 is engaged or disengaged. The flow of fluid from the passages25 takes place through openings or ports (e.g., bores) 28 in the member24. The radially inner portion of the member 24 is provided withimpressed or embossed portions 29 which constitute distancing elementsto maintain the neighboring portions of the piston 17 and the member 24at a selected distance from each other (as seen in the direction of theaxis 27 of the housing 2). The channels 18 a alternate with the embossedportions 29 and are configurated in such a way that the fluid issuingfrom the ports 28 flows in the respective channels 18 a substantiallyradially inwardly and into the compartment 18. The channels 18 a can besaid to constitute a circumferentially incomplete annular space which isinterrupted by the embossed portions 29 of the member 24. The fluidwhich enters the compartment 18 a (the latter is located between thecomponent or wall 9 of the housing section 4 and the sheet metal member24) is permitted to issue from the radially innermost portion of thecompartment 18 a as indicated by the arrows. The discharge ends thechannels 18 a are located radially inwardly of the rivets 17 r whichfixedly secure the neighboring portions of the members 17 and 24 to eachother so that the embossed portions or distancing elements 29 are urgedagainst the piston.

[0091] The piston 17 is provided with an embossed or impressed annularportion 30 which is located radially outwardly of the channel orchannels 18 a and also constitutes a distancing element between thepiston and the member 24. Such distancing element contributes to therigidity of the piston 17 and the member 24 in the region 19 of thefriction surface 21 and the friction lining 22. Furthermore, thedistancing element 30 establishes a radial seal between the members 17and 24.

[0092] When the lockup clutch 15 is engaged, the flow of fluid coolanttakes place from the second compartment 20, through the inlets 26, 26 a,through the passages 25, through the ports 28, through the channel orchannels 18 a and thence radially inwardly toward the hub 11 of theturbine 10. The fluid which leaves the compartment 18 at the hub 11 iscaused to flow through a channel in the hub 11 and/or through one ormore grooves in or at the hub 11 to enter a heat exchanger (not shown)wherein the heated fluid exchanges heat with another fluid prior tobeing admitted into a sump, from where it reenters the compartment 20 inthe housing 2. In other words, the fluid coolant is caused to flow alongan endless path from the compartment 20, into the compartment 18(subsequent to cooling of the wall 9 at the friction surface 21 and ofthe piston in the region of the friction lining 22) to thereupon reenterthe compartment 20.

[0093] The piston 17 and the member 24 (i.e., the members which definethe channel or channels 18 a) are connected to one another by the rivets17 r (which can be said to constitute or to form part of means forpreventing axial movements of the piston 17 in the direction of the axis27 in response to action of flowing fluid in the channel or channels 18a) in such a way that any axial component or components of the forcegenerated by the fluid in the channel or channels 18 a are neutralizedor taken up or counteracted by the member 24 so that the axial positionof the piston 17 remains unaffected by such forces. It is particularlyimportant that the aforediscussed axial component or components of theforce generated by cooling fluid in the channel or channels 18 a shouldnot cause any axial displacement of the piston 17 in a direction to theright (as viewed in FIG. 1), i.e., in a direction to reduce themagnitude of torque which can be transmitted between the frictionsurface 21 and the adjacent friction surface of the friction lining 22.Otherwise stated, the members 17, 24 and the rivets 17 r cooperate toensure that the member 24 and the piston 17 are propped or held relativeto each other in such a way that the power flow between these members isan endless flow, i.e., a flow which is closed in itself.

[0094] The just-outlined mode of causing the cooling fluid to prevent anoverheating of the wall 9 in the region of the friction surface 21and/or of the piston 17 in the region of its friction lining 22 withoutinitiating any undesirable reduction of the magnitude of torque which isbeing transmitted by the lockup clutch 15 is selected with a view totake into account the dynamics of cooling fluid flowing from thepassages 25, through the channel or channels 18 a, and into thecompartment 18 at the hub 11 of the turbine 10. Furthermore, thisdistinguishes the improved torque converter 3 and its lockup clutch 15from the corresponding constituents of the apparatus which is disclosedin the aforediscussed patent to Macdonald. The patentee discloses atorque converter and a lockup clutch or bypass clutch which are designedin such a way that the forces which are attributable to the dynamics ofthe cooling fluid are free to initiate a rise of fluid pressure so thatthe upper limit of the magnitude of torque which can be transmitted bythe lockup clutch of Macdonald decreases in response to increasing RPMof the housing of the patented torque converter. A pronounced reductionof the maximum torque which can be transmitted by the lockup clutch ofthe patented torque converter is attributable to the dynamics of coolingfluid which flows in the patented torque converter radially inwardlybetween the radially extending wall of the housing and the piston. Themagnitude of maximum torque which can be transmitted by the lockupclutch of Macdonald decreases as the rate of fluid flow radiallyinwardly between the housing of the patented torque converter and thepiston of its lockup clutch increases. Applicants believe that this isattributable, at least in part, to the effect of coriolis accelerationupon the fluid which flows radially inwardly between the housing of thepatented torque converter and the piston of its lockup clutch. Suchacceleration develops in response to rotation of the housing of thepatented torque converter and tends to impart to the fluid coolant acirculatory movement, while the fluid flows radially inwardly, to thusincrease the pressure of the fluid coolant.

[0095] In contrast to the construction and mode of operation of thepatented torque converter and its lockup clutch, the improved torqueconverter of FIG. 1 is designed to ensure that any rise of fluidpressure which develops as a result of radially inward flow of fluid inthe channel or channels 18 a and which can generate or actuallygenerates forces acting in the direction of the axis 27 cannot cause anyaxial shifting of the piston 17 from that position which has beenselected during transmission of torque from the housing section 4through the lockup clutch 15 and to the turbine 10. At any rate, theinfluence of axially oriented forces which act upon the piston 17 anddevelop as a result of radially inward flow of cooling fluid in thechannel or channels 18 a upon the axial position of the piston isincomparably less pronounced (and actually negligible) in comparisonwith the influence of such forces upon the ability of a conventionallockup clutch to transmit a desired torque.

[0096] In the torque converter 3 and the lockup clutch 15 of FIG. 1, theneutralization of the aforediscussed axially oriented forces is achievedby the establishment of the connection (by rivets 17 r) between themembers 17 and 24 which define the channel or channels 18 a andcooperate to ensure that any force or forces developing in a directionto move the friction lining 22 of the piston 17 axially and away fromthe friction surface 21 are counteracted by forces acting upon themember 24 in a direction to urge the friction lining 22 against thefriction surface 21.

[0097] The member 24 of the lockup clutch 15 shown in FIG. 1 extendsradially inwardly close to the hub 11 of the turbine 10, i.e., thechannel or channels 18 a are rather long (as measured radially of theaxis 27). However, it is equally within the purview of the invention toreplace the member 24 with a member whose radially inner portion islocated radially outwardly of the radially inner portion of the piston17, i.e., the radial length of the channel or channels 18 a can be less,and even substantially less, than that of the channel 18 a which isshown in FIG. 1. This may be advisable if the designer of the torqueconverter 3 and its lockup clutch 15 desires to ensure that apredictable change of the magnitude of torque transmitted by the lockupclutch will take place in response to increasing RPM of the housing 2,i.e., in response to increasing rate of fluid flow from the compartment20 into the compartment 18. It has been found that, at least in many ormost instances, it is advisable to construct the lockup clutch 15 insuch a way that the length of each channel 18 a (as measured radially ofthe axis 27) is not less than 50% of the width of the compartment 18,i.e., not less than 50 percent of the width of the piston 17.

[0098] It is further possible to modify the structure of FIG. 1 so thata portion of the fluid which is to cool the housing 2 in the region ofthe wall 9 and the piston 17 in the region of the friction lining 22flows from the compartment 20 into and through the channel or channels18 a and the remaining portion of the fluid flows from the compartment20 through the section 18 b of the compartment 18, i.e., radiallyinwardly through that section which is disposed between the wall 9 andthe member 24 (as seen in the direction of the axis 27). The channel orchannels 18 a constitute the other section of the compartment 18. Allthat is necessary is to provide one or more openings in the member 24 sothat they permit the fluid to flow between the sections 18 a and 18 b ofthe compartment 18. The combined area of the openings and/or theirradial distance from the axis 27 will be selected in dependency upon thedesired effect upon the cooling of certain parts of the torque converter3 and its lockup clutch 15 and/or upon the magnitude of torque to betransmitted by the lockup clutch during certain stages of operation ofthe improved apparatus.

[0099] In the diagram of FIG. 2, the RPM of the housing 2 is measuredalong the abscissa (at n), and the relationship M/Δp of torque which canbe transmitted by the lockup clutch to the pressure differential offluid at opposite sides of the piston is measured along the ordinate.The curve 31 denotes the relationship of transmitted torque to the RPMof the housing for a preselected constant pressure differential betweenthe fluids at the opposite sides of a piston forming part of aconventional lockup clutch, namely a clutch which is designed to preventthe flow of fluid between the spaces or compartments at opposite sidesof the piston. The curve 31 indicates that, if Δp is constant, themagnitude of torque transmittable by the engaged lockup clutch in aconventional torque converter remains at least substantially unchanged.Torque converters utilizing such lockup clutches are disclosed, forexample, in U.S. Pat. No. 4,649,763.

[0100] The curve 32 denotes in FIG. 2 the magnitude of torque which canbe transmitted by the lockup clutch 15 in the torque converter 3 of FIG.1 in response to changes of the RPM and at a constant pressuredifferential Δp between the fluids in the compartments 18, 20 and whilethe fluid is free to flow from the compartment 20 into the compartment18 along the aforementioned path including the passages 25 and thechannels 18 a. Torque converters which include lockup clutches capableof transmitting torque in a manner as denoted by the curve 32 aredisclosed, for example, in U.S. Pat. No. 4,445,599 (granted May 1, 1984to Bopp for “Cooling Means For Torque Converter Bypass”) and in U.S.Pat. No. 5,056,631 (granted Oct. 15, 1991 to Macdonald for “SlippingBypass Clutch Construction For A Hydrokinetic Torque Converter”). Thepatents disclose lockup clutches wherein the piston (pressure plate)and/or the counterpressure plate is provided with channels or openingsdisposed in the region of the friction lining or friction linings andpermitting fluid coolant to flow from a compartment for the pump andturbine of the torque converter into a compartment between the pistonand a wall of the housing of the torque converter. The establishment ofa path for such flow of fluid in the patented torque converters entailsthat, when the value of Δp is constant, the maximum torque which can betransmitted by the lockup clutch decreases in response to increasingRPM. This is due to losses of fluid in the path or paths from thecompartment for the turbine into the other compartment as well as tofluid losses along the path from the other compartment back into thecompartment for the turbine. Additional losses develop during fluid flowthrough the lockup clutches of the patented torque converters. The curve32 indicates that, for a selected value of Δp and at a low RPM, themaximum torque denoted by the curve 32 is less than the torque denotedby the curve 31. Furthermore, dynamic losses are superimposed upon thestatic losses so that the maximum torque transmittable by a lockupclutch as denoted by the curve 32 is even less. Dynamic losses aregenerated as a result of radially inward flow of fluid from thecompartment for the turbine toward and into the other compartment. Thisis also shown in FIG. 2 wherein dynamic losses cause the curve 32 toslope downwardly toward the abscissa when the value of Δp is constantbut the RPM of the housing of the torque converter increases.

[0101] The broken-line curve 33 denotes in FIG. 2 the torque which isbeing transmitted by the improved lockup clutch 15 of the presentinvention at a constant value of Δp. It will be noted that the maximumvalue of transmitted torque at a lower RPM and at a constant Δp is thesame as that denoted by the left-hand portion of the curve 32. However,the maximum transmittable torque (by the lockup clutch of the presentinvention) remains unchanged whereas the maximum torque denoted by thecurve 32 decreases due to pronounced influence of dynamic losses whenthe housing of the torque converter is rotated at a higher speed.

[0102] Of course, the characteristic curve denoting the maximum torquewhich can be transmitted by the improved lockup clutch 15 in theimproved torque converter 3 of FIG. 1 can depart from the broken-linecurve 33 in the diagram of FIG. 2. For example, the maximum value oftransmittable torque may decrease at a certain rate in response toincreasing RPM of the housing 2 of the torque converter 3. Nevertheless,it is now possible (by properly selecting the rate and the direction offluid flow in the channel or channels 18 a) to ensure that the curve 33departs from an ideal curve solely as a result of static losses, i.e.,that any dynamic losses developing when the lockup clutch 15 is in usedo not affect the maximum transmittable torque at a selected constantvalue of Δp. At any rate, the influence of dynamic Δp losses upon thetransmission of torque by the engaged friction clutch 15 at a given Δpis nil or not more than a minute fraction of the dynamic losses whichdevelop when the transmission of torque is carried out by a conventionallockup clutch.

[0103] It is to be noted that the curves 31, 32 and 33 in the diagram ofFIG. 2 were plotted without taking into consideration certain otherparameters, such as friction within the conveyed fluid and/or frictionbetween the flowing fluid and the adjacent surfaces.

[0104]FIG. 3 illustrates a portion of a torque converter which embodiesa modified lockup clutch 115. As can be seen in FIG. 1, the radiallyoutermost portion 17 a of the piston 17 is adjacent the radially outerportion of the member 24. On the other hand, the radially outermostportion of the member 124 in the lockup clutch 115 of FIG. 3 extendswell beyond the radially outer portion of the piston 117 and includes arelatively short tubular or cylindrical part which is closely adjacentthe internal surface of the surrounding portion of the housing 102 ofthe lockup clutch. Furthermore, the radially innermost portion of thepiston 117 is not mounted on the hub 111 of the turbine for movement inthe axial direction of the housing 102. The member 124 is centered byand has limited freedom of axial movement relative to the hub 111. Itcan be said that the actual piston or pressure plate of the lockupclutch 115 of FIG. 3 is the member 124 and that the member denoted bythe character 117 serves as a reinforcement or stiffener for the member124.

[0105] The flow of fluid from the compartment 120 at one side into thecompartment 118 at the other side of the composite piston including themembers 117, 124 is indicated by arrows. Here, again, the fluid whichflows radially inwardly in the channel or channels 118 a is compelled toact upon the members 117 and 124 (these members are riveted to eachother, as at 117 r) in such a way that it cannot generate forces, whichwould reduce the ability of the clutch to transmit torque from thehousing to the turbine in the engaged condition of the clutch. Otherwisestated, the fluid which flows radially inwardly in the channel orchannels cannot compel the piston to move axially of and away from theadjacent radial wall of the housing 102, i.e., in a direction to reducethe magnitude of transmitted torque in response to increasing RPM of thehousing 102. Thus, the lockup clutch 15 or 115 is capable of at leastsubstantially neutralizing dynamic forces which develop during flow offluid coolant from the compartment 120 radially inwardly toward andthrough the channel or channels 118 a and into the compartment 118.Accordingly, the curve 33 of FIG. 2 denotes the torque which is beingtransmitted by the engaged lockup clutch 15 or 115.

[0106] As used herein, the term channel or channels is intended toembrace discrete grooves, tunnels or analogous paths establishingrecesses, bores, holes or cavities as well as circumferentially completeor incomplete chambers or spaces which enable the fluid to flow radiallyinwardly from the region of the friction lining or linings toward thesecond compartment 18 or 118. A circumferentially incomplete channel canbe composed of several individual channels which may, but need not,communicate with one another. Still further, the member 17 and/or themember 24 of FIG. 1, as well as the member 117 and/or 124 of FIG. 3, cancarry a set of discrete pipes or tubes which define the channels for theflow of fluid coolant from the passage or passages at the frictionlining 22 or 122 into the compartment 18 or 118. The radially innermostportions of the pipes can discharge the conveyed fluid directly into thecompartment 18 or 118 or into one or more channels or grooves in the hub11 or 111 wherein the fluid flows toward and through a suitable coolingsystem (e.g., one or more heat exchangers) and thence into a sump to bereturned into the compartment 20 or 120. Still further, it is possibleto provide one or more tubular members in compartment 20 or 120 todirect the fluid toward and into the passages 25 of the lockup clutch 15or into analogous passages of the lockup clutch 115.

[0107] The passages 25 in the clutch 15 of FIG. 1 and/or the passages ofthe clutch 115 need not necessarily be provided in the friction lining22 or 122. Thus, it is equally possible to provide such passages in thewall 9 of the housing 2 of FIG. 1 and/or in the corresponding wall ofthe housing 102. Still further, passages in the friction lining of alockup clutch can be provided in addition to passages in the housing 2or 102.

[0108] The construction of the clutch 115 is such that the member 117need not be provided with openings corresponding to the inlets 26 a inthe piston 17 of FIG. 1; however, it is necessary to provide one or moreopenings (not referenced) in the member 124 of FIG. 3 in order to enablethe fluid to flow from the channel or channels 118 a into thecompartment 118. The openings 26 and/or the openings 28 and/or theopenings in the member 124 can be designed with a view to influence thefluid in a manner corresponding to that of orifices of discrete nozzles.For example, the surfaces bounding such openings can be configurated tothrottle the flow of the fluid therein.

[0109] As already mentioned above, the friction lining 22 can beprovided on the wall 9 or this wall can carry an additional frictionlining which provides the friction surface 21. Analogously the frictionlining 122 shown in FIG. 3 can be provided on the member 124 or on theadjacent portion of the housing 102, or the lockup clutch 115 can employtwo friction linings, one on the composite piston including the members117, 124 and the other on the adjacent radial wall of the housing 102.

[0110] Each friction lining can be bonded (e.g., adhesively secured) tothe respective carrier. The passages in the friction linings can beformed by impressing them into the friction surfaces of the frictionlinings and/or by removing some material from the friction surfaces.Furthermore, each passage (such as the passage 25 shown in FIG. 1) canbe provided in part in a friction lining and in part in the adjacentfriction surface, such as the friction surface of the wall 9 formingpart of the housing 2 shown in FIG. 1. It has been found that thepassages in the friction surfaces of friction linings and/or in thefriction surfaces which are contacted by friction linings when thelockup clutch is engaged ensure a highly satisfactory exchange of heatbetween the friction surfaces and the fluid coolant to thus ensure thatthe parts which are provided with friction surfaces as well as the fluidare not subjected to excessive or even very pronounced thermal stresses.

[0111] The provision of inlets (such as 26) close to the radiallyoutermost portions of the friction surfaces and of the outlets (such as28) close to the radially innermost portions of the friction surfacesalso contributes to highly satisfactory and uniform dissipation of heatby the parts which carry the friction surfaces. The feature that thechannel or channels (18 a, 118 a) are relatively long (preferably notless than half the width of the compartment 18 or 118) is desirable andadvantageous because this even further reduces the likelihood of thedevelopment of unbalanced axial stresses which would tend to move thepiston of the engaged lockup clutch in a direction to reduce themagnitude of torque which is to be transmitted from the housing to theturbine of the torque converter.

[0112]FIG. 1 shows that the path of fluid from the compartment 20 intothe compartment 18 extends through the inlets 26, 26 a of a passage 25and thereupon through the respective outlet 28 which includes openingsin the friction lining 22 and in the member 17. However, it is equallypossible to extend the passages 25 all the way to the radially innermostportion of the friction lining 22 so that the establishment of an outletthen merely necessitates the provision of a hole or opening in themember 24 radially inwardly of the friction lining 22. In other words,fluid which issues from a passage 25 need not flow through the frictionlining 22 prior to traversing the member 24 on its way into the radiallyouter portion of a single channel 18 a or one of several channels.

[0113]FIG. 4 shows certain details of a portion of a lockup clutch 215which is installed in the housing of a torque converter in such a waythat the channel or channels 218 a are disposed between the piston 217and the member 224 at that side of the piston which faces away from thewall 209 of the housing. Otherwise stated, the piston 217 is installedbetween the member 224 and the wall 209. The member 224 can constitute aconverted blank of metallic sheet material and includes a washer-likecentral portion, a frustoconical radially outer portion and asleeve-like radially inner portion. The passages 225 are providedbetween the frustoconical radially outer portion of the piston 217 andthe adjacent frustoconical portion of the wall 209. The outlet of eachpassage 225 communicates with the radially outer portion of a singlechannel 218 a or one of several channels by way of a port 228 in thepiston 217. Each passage 225 is provided in the friction lining 222. Theradially innermost portion of each channel 218 a communicates with theadjacent portion of the compartment 218 by way of one or more axiallyparallel openings 234 in the piston 217. It will be noted that thecompartment 218 extends radially of the axis of the housing of thetorque converter intermediate the wall 209 of the housing and theadjacent side of the piston 217.

[0114] Not only the channel 18 a which is shown in FIG. 1 or the channel118 a which is shown in FIG. 3 but also the channel 218 a shown in FIG.4 can constitute an annular chamber extending all the way around theaxis of the housing of the torque converter between the confrontingsurfaces of the piston 17, 117 or 217 and the member 24, 124 or 224. Ifthe improved lockup clutch is provided with a number of channels toestablish paths between the passages in a friction lining and the firstcompartment, the member 24, 124 or 224 can be replaced with one or moretubular members which convey the fluid from the passages into the firstcompartment of the respective torque converter. By way of example, themember 24 of FIG. 1 or the member 224 of FIG. 4 can be replaced with oneor more tubes which establish paths for the flow of fluid from thepassages 25 or 225 into the compartment 18 or 218.

[0115] The outlets of the passages in a friction lining need notdischarge the fluid coolant into a first compartment (such as thecompartment 218) or into a section (such as 18 b) of the firstcompartment. Instead, the outlets of the passages can discharge fluidinto one or more radially extending bores in the hub of the turbine(such as the hub 11 of the turbine 10 which is shown in FIG. 1), and thehub then surrounds a conduit or other suitable means for conveying theheated fluid into a heat exchanger.

[0116]FIG. 5 shows a portion of a hydrokinetic torque converter 303which includes a modified lockup clutch 315. The piston 317 of theclutch 315 divides the chamber of the housing 302 into a firstcompartment 318 and a second compartment 320. The piston 317 is movablein the axial direction of the housing 302 and is centered by the hub 311of the turbine in the housing 302. A damper 316 is interposed betweenthe piston 317 and the turbine to transmit torque from the housing 302to the hub 311 when the lockup clutch 315 is engaged. The illustrateddamper 316 includes a set of arcuate energy storing elements in the formof coil springs, an input member which is of one piece with or iscarried by the piston 317, and an output member which is of one piecewith or is carried by the turbine or its hub 311.

[0117] When the clutch is engaged and the housing 302 of the torqueconverter 303 is driven by a prime mover, such as a combustion engine ina motor vehicle, the fluid coolant is caused to flow from thecompartment 320 and at least substantially radially inwardly toward andinto the compartment 318. The fluid in the compartment 318 flowsradially inwardly between the wall 399 of the housing 302 and the member324 which is affixed to the hub 311. The passages 325 at the frictionlining 322 have inlets 326 which are provided in nozzles 326 a (oneshown in FIG. 5) installed in and close to the radially outermostportion of the piston 317. The illustrated nozzle 326 a acts not unlikea flow restrictor and the jet or stream of fluid issuing from itsorifice 326 (i.e., from the inlet of the respective passage 325)impinges upon the friction surface 321 of the wall 309 forming part ofthe housing section 304 as well as upon the friction surface of thefriction lining 322. The region of the two friction surfaces isidentified by the character 319 and is disposed between frustoconicalportions of the wall 309 and piston 317. The passages 325 are or can beprovided in the friction lining 322 and/or in the friction surface 321of the wall 309. Each passage 325 discharges the fluid directly into theradially outermost portion of the compartment 318, and such radiallyoutermost portion can be said to constitute a channel which directs theinflowing fluid radially inwardly toward the axis of the housing 302.

[0118] Even though the member 324 is nonmovably affixed to the hub 311of the turbine while the piston 317 is free to move (within limits)relative to the hub 311 in the axial direction of the housing 302, thefluid flowing radially inwardly within the compartment 318 cannot causeundesirable axial shifting of the piston 317. This is due to the factthat any and all axially oriented components of the force generated bythe fluid in the compartment 318 are taken up by the member 324 which isaffixed to the hub 311 against movement in the axial direction of thehousing 302.

[0119] In lieu of affixing the member 324 to the hub 311 of the turbine,it is equally possible to affix this member to the housing 302 in such away that the member 324 cannot move or cannot yield in the axialdirection of the housing. All that counts is to ensure that the fluidflowing radially inwardly from the passages in the region of thefriction surfaces toward and into one or more channels of or leadinginto the first compartment cannot cause any undesirable axial shiftingof the piston in a direction to disengage the respective lockup clutchor to reduce the magnitude of torque which is to be transmitted by thelockup clutch.

[0120] The passages can be provided in the friction lining on the pistonof the lockup clutch, in the friction surface of the housing, in thepiston itself and/or even in the member which cooperates with the pistonto define one or more channels connecting the passages with the firstcompartment. For example, it is within the purview of the invention toprovide one or more passages in the member 24 of the lockup clutch 15 orin the member 124 of the lockup clutch which is illustrated in FIG. 3. Apiston which forms part of a lockup clutch or bypass clutch and isprovided with one or more passages for the flow of oil is disclosed inthe aforementioned U.S. Pat. No. 5,056,631 to Macdonald.

[0121] Those novel features of a hydrokinetic torque converter and itslockup clutch which were described with reference to FIGS. 1 to 5 can beembodied with equal or similar advantage in many other types of torqueconverters and lockup clutches. For example, the aforediscussed featureof causing the fluid to flow radially inwardly past the frictionsurfaces of the clutch and the provision of means for preventing axialmovements of the piston in the direction of the axis of the housing ofthe torque converter in response to the action of fluid in the channelor channels leading the fluid from the passages at the friction liningsinto the first compartment of-the chamber defined by the housing can beput to use by properly modifying certain heretofore known torqueconverters, for example, those described and illustrated in U.S. Pat.Nos. 4,493,406 and in 4,445,599.

[0122]FIG. 6 shows a friction lining 422 which resembles a split ringand can be put to use in the improved lockup clutch, e.g., in lockupclutches of the type described with reference to FIGS. 1 and 3 to 5. Thefriction lining 422 comprises a continuous arcuate radially outerportion 422 a and a continuous arcuate radially inner portion 422 b. Thearcuate central portion 422 b of the friction lining 422 is providedwith a plurality of substantially meandering or zig-zag shaped passages435 in the form of cutouts or depressions in the friction surface, i.e.,in that surface which contacts the other friction surface when thelockup clutch embodying the friction lining 422 is engaged.

[0123] Each of the several passages 435 has an inlet 439 at the radiallyouter portion 422 a and an outlet 440 at the radially inner portion 422b of the friction lining 422. The illustrated nine passages 422 togetherconstitute a composite arcuate passage which extends along an arc ofnearly or exactly 360° when the friction lining 422 is bonded orotherwise affixed to the piston or to the other component which carriesa friction surface, e.g., to the piston 17 or to the wall 9 of thehousing 2 in the torque converter 3 of FIG. 1.

[0124] An advantage of an uninterrupted or continuous passage or of acomposite passage (such as the one including passages 435 of the typeshown in FIG. 6) is that the fluid is compelled to flow along anelongated path and to thereby withdraw large amounts of heat from theadjacent portion of the piston or the other component which carries afriction surface. This reduces the thermally induced stresses upon thepiston and the adjacent component of the lockup clutch as well as uponthe fluid coolant.

[0125] The length and the configuration of the passages 435 in thefriction lining 422 are preferably selected in such a way that theresistance to the flow of fluid coolant therein is satisfactory evenunder the most difficult or adverse circumstances of use of the lockupclutch and the torque converter in which the clutch is put to use. Inother words, even if the fluid is being heated to a maximum permissibletemperature, the rate of fluid flow between the compartments at oppositesides of the piston should not exceed that value at which the systempressure in the torque converter is likely to collapse. It is preferredto select the rate of fluid flow in the passages 435 in such a way thatit is not unduly influenced by the temperature of the fluid, i.e., thatthe rate of fluid flow between the two compartments can or may fluctuatedepending upon variations of certain parameters of the torque converter,the prime mover which drives the torque converter and/or the unit orunits which receive torque from the torque converter, but should not bedependent, or should not be overly dependent, upon the fluctuations ofthe temperature of fluid coolant.

[0126] The nine illustrated passages 435 in the friction surface of thefriction lining 422 of FIG. 6 have identical dimensions and identicalshapes and are equidistant from each other when the friction lining isbonded to a frustoconical portion of the piston or to a frustoconicalportion of the adjacent wall of the housing or to a frustoconicalportion of a member corresponding to the member 24 in the torqueconverter of FIG. 1. The number of discrete passages 422 can be reducedto less than nine or increased to ten or more, but is preferably notless than three.

[0127] When bonded to a frustoconical surface (such as the left-handside of the conical radially outer portion of the member 24 in thelockup clutch 15 of FIG. 1), the split friction lining 422 preferablyconstitutes a circumferentially complete hollow conical frustum. Inother words, the two end portions 436 and 437 of the friction lining 422are then closely or immediately adjacent each other or actually abut oneanother.

[0128] A friction lining of the type shown in FIG. 6 can be replaced bya friction lining which is assembled of two or more arcuate sections 438of the character shown in FIG. 7. This reduces waste in the material ofwhich the sections 438 are made. Each of the illustrated arcuatesections 438 is provided with a set of three identical passages 435. Thesegments 438 are bonded or otherwise secured to the piston, to the wallof the housing or to another member (such as 24) of the torque converterso that they jointly constitute a hollow frustoconical friction lining.

[0129] The manipulation of the arcuate sections 438 can be simplified byapplying an adhesive-coated foil to one side of the blank from which thesections are removed, e.g., in a stamping or another suitable machine.The application of such foil is facilitated because the one side of theblank is smooth, i.e., it need not be provided with passages 435 or withotherwise configurated and/or dimensioned passages. The provision ofcontinuous radially inner and radially outer portions 422 a, 422 b onthe friction lining 422 of FIG. 6 and of continuous radially inner andradially outer portions on the sections 438 of FIG. 7 also facilitatesthe manipulation of such friction lining or such sections prior to aswell as during bonding to a carrier such as the piston of the improvedlockup clutch.

[0130] It is clear that if, for example, the piston of the improvedlockup clutch is to be provided with a friction lining of the type shownin FIG. 6 or 7, the piston must be provided with suitably distributedinlets (such as 26 or 226 or 326) to establish paths for the flow offluid coolant into the inlets 439 of the passages 435 in the frictionlining. Furthermore, it is necessary to establish paths (e.g., bores,holes, slots or the like) for the flow of fluid from the outlets 440 ofthe passages 435 into the channel of channels serving to cause the fluidto flow radially inwardly into the first compartment of the housing ofthe torque converter. Alternatively, the piston or another componentwhich carries a friction lining of the type shown in FIG. 6 or 7 can beprovided with grooves which receive fluid from the passages 435, i.e.,such carrier of the friction lining need not be provided with bores,holes or slots which extend all the way between the two sides of thecarrier. For example, the ports 228 in the piston 217 of FIG. 4 can beomitted if the left-hand side of the piston is provided with groovesreceiving fluid streams from the outlets 440 of passages 435 of the typeshown in FIG. 6 or 7. FIG. 5 shows, by broken lines, a groove 441 in theleft-hand side of the frustoconical portion of the piston 317; suchgroove is angularly offset relative to the respective inlet 326 anddirects fluid coolant into the compartment 318.

[0131] It is presently preferred to configurate the passages 435 in sucha way that each passage includes at least two turns which alter thedirection of fluid flow from a direction toward the radially outerportion (such as 422 a) toward the radially inner portion (such as 422b) of the respective friction lining (such as 422). Each of theillustrated passages 435 has six turns, i.e., a total of seven straightor substantially straight portions (depending upon whether the passagesare zig-zag shaped or substantially zig-zag shaped, such as sinusoidal,snake-like or meandering). For example, each of the illustrated zig-zagshaped passages 435 can be replaced by a sinusoidal or snake-likepassage having a series of six concave-convex portions.

[0132]FIG. 8 illustrates a portion of a torque converter wherein thepiston 417 of the lockup clutch carries a friction lining 422 identicalwith or resembling the friction lining of FIG. 6. The friction lining isbonded to the left-hand side of the frustoconical portion of the piston417 opposite the adjacent frustoconical portion of the wall forming partof the section 404 of the housing 402 of the torque converter. Thesection 404 has an axially extending circumferential internal shoulder402 a at the radially inner end of the illustrated passage 435. Theshoulder 402 a bounds one side of the radially outermost portion of thechannel forming part of or leading into the compartment 418. In otherwords, the shoulder 402 a is located opposite the outlets 440 of grooves435 in the friction lining 422.

[0133] In order to reduce the influence of the temperature and/orviscosity of the fluid coolant, as well as the influence of the pressuredifferential between the two compartments in the housing of the torqueconverter, upon the rate of fluid flow between the two compartments, afurther feature of the present invention resides in the provision of oneor more devices constituting means for regulating the rate of fluid flowalong the friction surfaces of the lockup clutch by taking intoconsideration the variations of the aforementioned parameters, such asthe temperature and viscosity of the fluid and the difference betweenthe pressures in the two compartments of the housing of the torqueconverter. The regulating means can vary the rate of fluid flow independency upon one or more of the aforediscussed parameters.

[0134] The regulating means can comprise one or more adjustable valves542 of the type shown in FIGS. 8a and 9. The illustrated valve 542 iscarried by the piston 517 and comprises a body or housing 543 located atthat side of the piston 517 which faces away from the friction lining522. To this end, the body 543 comprises a short annular portion 544which is received in a complementary bore or socket 545 of the piston517. For example, the portion 544 can be a press fit in the socket 545.

[0135] As best shown in FIG. 9, the body 543 of the valve 542 defines achamber 552 for a reciprocable piston or plunger 546 (hereinafter calledplunger to distinguish from the piston 517 of the lockup clutch). Theplunger 546 is provided with an axial extension 547 which isreciprocable in an opening 548 provided in a sleeve 550 which isinstalled in the body 543. Opening 548 constitutes the outlet of a pathfor the flow of fluid coolant through the body 543. The rate of fluidflow through the body 543 can be altered by changing the axial positionof the plunger 546 in the chamber 552. To this end, the extension 547 ofthe plunger 546 is configurated to ensure that the rate of fluid flowthrough one or more substantially axially parallel grooves 549 of theextension 547 is altered in response to shifting of the plunger 546toward or away from the bottom wall or end wall 554 of the body 543. Thebody 543 is further provided with two or more tubular inlets 555 whichadmit the fluid coolant into the groove or grooves 549 of the extension547. It is also possible to configurate the surface bounding the opening548 in the sleeve 550 in such a way that the rate of fluid flow from thevalve 542 into the respective passage 535 can be altered in apredictable manner in response to axial displacement of the piston 546in the cylinder chamber 552.

[0136] The sleeve 550 is a press fit or is otherwise securely held inthe body 543 and includes a smaller-diameter extension 551 in thechamber 552. The sleeve 550 and its extension 551 constitute a retainerfor one end portion of a counterbalanced coil spring 553 which bearsupon the larger-diameter portion of the plunger 546 so that the plungeris urged toward the bottom end wall 554 i.e., in a direction to increasethe rate of fluid flow through the body 543.

[0137] The valve 542 increases the rate of fluid flow through itshousing 543 when the difference between the fluid pressures in the twocompartments in the housing including the section 504 of FIG. 8a isrelatively small.

[0138] The inlets 555 admit fluid from the second compartment of thehousing including the section 504 into the inlet of the respectivepassage 535 at the radially outer portion of the area 519 of frictionalengagement between the friction lining 522 and the section 504 in theengaged condition of the lockup clutch. It is also possible to installthe valve 542 and to configurate the piston 517 in such a way that thevalve can admit fluid coolant to two or more passages 535.

[0139] The configuration of the groove or grooves 549 in the extension547 of the plunger 546 is such that the rate of fluid flow from theinlets 555 to the opening 548 is reduced in response to shifting of theplunger in a direction to the left, i.e., so as to move the extension547 deeper into the opening 548. Furthermore, the characteristic of thespring 553 is such that, in conjunction with appropriate shaping of thesurface(s) surrounding the groove(s) 549, the valve 542 automaticallyregulates the rate of fluid flow through the valve so that the rate isconstant during each stage of operation of the torque converter.Furthermore, the valve 542 renders it possible to ensure that the rateof fluid flow into the respective passage or passages 535 is at leastsubstantially independent of the pressure differential in thecompartments at opposite sides of the piston 517.

[0140] However, it is equally possible to design the valve 542 (e.g., byappropriate shaping of the surface(s) bounding the groove(s) 549 and/orby appropriate dimensioning of the cross-sectional area of the opening548 and/or by appropriate selection of the characteristic curve of thespring 553) in such a way that one can select any one of an array ofdifferent characteristic curves for the rate of fluid flow through thevalve. For example, the valve 542 can be designed in such a way that therate of fluid flow through the body 543 is gradually increased orgradually reduced in response to increasing difference between the fluidpressures in the two compartments of the housing of the torqueconverter. If desirable or necessary, the valve 542 or an analogousfluid flow regulating device can be designed and installed in such a waythat the flow of fluid in the passage(s) 535 is completely interruptedwhen the pressure differential between the two compartments rises to apredetermined value. However, at least in most instances, it isadvisable or sufficient to design the valve 542 or its equivalent insuch a way that the rate of fluid flow from the second compartment intothe passage(s) 535 is at least substantially constant, i.e., that it ispractically independent of fluctuations of pressure of fluid coolant inthe first and/or the second compartment, such as at the inlets 555 ofthe valve body 543. A valve which regulates the rate of fluid flow witha view to avoid any, or any appreciable, changes in response to changesof the difference between the fluid pressures in the two compartmentsexhibits the additional advantage that it can be readily designed andinstalled in such a way that the rate of fluid flow from the inlets 555to the opening 548 is at least substantially independent of fluctuationsof the temperature of the conveyed fluid.

[0141]FIG. 8a shows that the valve 542 is installed at the inlet 539 ofthe passage 535 in the friction lining 522 which is bonded to the piston517.

[0142]FIG. 9a illustrates a modified fluid flow regulating valve 642which can be utilized in lieu of the valve 542. All that is necessary isto alter the socket in the piston or another component of the torqueconverter so that the body 643 of the valve 642 can be a press fit or isotherwise securely held therein. The valve 542 or 642 can also be usedas a substitute for the nozzle 326 a which is shown in FIG. 5. The body643 defines a cylindrical chamber 652 for a reciprocable plunger 646.The chamber 652 is a blind bore or hole in the body 643, and its openend is partially sealed by a washer-like insert 650 defining a centralopening 650 a constituting the inlet of the valve 642. A calibratedresilient element 653, such as a coil spring, is installed in thecylinder chamber 652 to react against the bottom end wall 654 and tobear upon the plunger 646 in order to urge the plunger toward the insert650. FIG. 9a shows that the left-hand end face of the plunger 546 isprovided with a recess 646 a for a substantial number of convolutions ofthe spring 653. The plung 646 divides the cylinder chamber 652 into afirst section 652 a at the insert 650 and a second section 652 b at theend wall 654.

[0143] The section 652 a of the cylinder chamber 652 receives fluidcoolant by way of the central opening 650 a in the insert 650. Thepressure of fluid entering the cylinder chamber section 652 acorresponds to fluid pressure in the second compartment of the housingof the torque converter, i.e., in that compartment which accommodatesthe turbine and the pump. The left-hand section 652 b of the cylinderchamber 652 receives fluid through a flow restricting channel or orifice657 in the plunger 646. The orifice 657 serves as a means forestablishing a pressure differential Δp between the sections 652 a and652 b of the cylinder chamber 652. The orifice 657 is in series with aregulating orifice 658 which is provided in the valve body 643 andserves to regulate the rate of fluid flow into one or more passagesdepending upon the pressure of fluid in the section 652 a of thecylinder chamber 652. This is achieved in that, by properly selectingthe cross-sectional area of the regulating orifice 658, one can select apredetermined value for the pressure differential Δp. As already pointedout hereinbefore, it is normally advisable and desirable to regulate therate of fluid flow in such a way that it remains at least substantiallyconstant. The illustrated regulating orifice 658 is composed of a set ofradially extending ports 648 in the body 643 of the valve 642. Theeffective combined cross-sectional area of the ports 648 is changed inresponse to axial displacement of the plunger 646 in the cylinderchamber 652.

[0144] When the fluid pressure in the section 652 a of the cylinderchamber 652 rises, the plunger 646 is displaced in a direction to theleft, as viewed in FIG. 9a, i.e., in a direction to stress the valvespring 653, so that the combined effective cross-sectional area of theports 648 is reduced accordingly. This, in turn, entails a rise of fluidpressure in the section 652 b of the cylinder chamber 652 so that thepressure differential is altered in a direction to ensure that the rateof fluid flow from the cylinder chamber section 652 b into the ports 648matches the desired value. Each port 648 can discharge a fluid coolantinto a discrete passage or all of the ports 648 in the body 643 of thevalve 642 can admit fluid into the inlet of a single passage.

[0145]FIG. 10 illustrates a portion of a hydrokinetic torque converterincluding a lockup clutch 715 having a friction lining 722 bonded orotherwise affixed to the right-hand side of a substantiallyfrustoconical component 704 a riveted (as at 760) or otherwise affixedto the wall 709 of the section 704 of a composite housing which can beconstructed in the same way as the housing 2 of the torque converter 3shown in FIG. 1. The component 704 a can be made of metallic sheetmaterial and the friction surface of its lining 722 confronts thefriction surface at the radially outermost portion of the piston 717.

[0146] The rivets 760 can constitute separately produced parts; however,and as actually shown in FIG. 10, each rivet 760 can also constitute asuitably displaced or depressed portion of the radially extending wall709 of the housing section 704. Each displaced portion of the wall 709is received in a complementary socket or recess at the adjacent side ofthe wall 704 a.

[0147] The left-hand frustoconical surface of the wall 704 a defineswith the adjacent portion of the wall 709 an intermediate space 761having a substantially wedge-shaped cross-sectional outline. The space761 contains at least one fluid flow regulating valve 742 which ismounted on the wall 704 a, and this space communicates with the secondcompartment of the chamber within the housing including the section 704.It can be said that the space 761 constitutes an extension of the secondcompartment.

[0148] The radially outermost portion of the wall 704 a can be providedwith an annularly arranged set of lugs, prongs or other protuberanceswhich are anchored in the adjacent cylindrical portion of the housingsection 704. Alternatively, the prongs, tongues or other protuberancescan be provided at the inner side of the housing section 704. In eitherevent, the prongs of the wall 704 a and/or of the housing section 704are distributed in such a way that they establish adequate paths for theflow of fluid from the second compartment of the housing into the space761 or from the major part of the second compartment into the smallerpart or space 761. The feature that the wall 704 a is in engagement withthe adjacent portion of the housing section 704 ensures that the wall704 a is highly unlikely to undergo any, or any appreciable, deformationwhich could result in undesirable axial shifting of the piston 717 underthe action of axial forces generated by the fluid flowing from thepassages 725 into one or more channels and thence into the firstcompartment.

[0149] The friction surface of the piston 717 is provided on afrustoconical portion 730 which is adjacent the friction surface of thefriction lining 722 on the wall 704 a. When the lockup clutch 715 isengaged, fluid coolant can flow from the space 761 into the valve orvalves 742 and thence into the passages 725. These passages are providedin the friction lining 722. The valve 742 of FIG. 10 is or can beidentical with the valve 542 of FIGS. 8a and 9 or with the valve 642 ofFIG. 9a.

[0150]FIG. 11 shows a portion of still another hydrokinetic torqueconverter having a lockup clutch including a piston 817. A frustoconicalportion of the piston 817 carries a friction lining 822 having passages825 with inlets in communication with substantially axially parallelholes or bores 826 machined into or otherwise formed in the piston. Asingle valve 842 (corresponding to one of the valves described withreference to FIGS. 8a, 9 and 9 a) suffices to regulate the fluidpressure at the inlets of a plurality of identical or different passages825 in the friction surface of the lining 822. To this end, the outletof the valve 842 discharges fluid into an annular space 863 between theright-hand side of the piston 817 and the left-hand side of a member 862which is carried by the piston. The inlets of the passages 825communicate with the annular space 863 by way of the respective bores orholes 826 in the piston 817. FIG. 11 shows that the valve 842 isinstalled radially inwardly of the bores or holes 826, i.e., the fluidwhich enters the space 863 between the member 862 and the piston 817must flow radially outwardly on its way into the inlets of the passages825.

[0151] It is clear that the torque converter embodying the structure ofFIG. 11 can comprise two or more suitably distributed valves 842.Nevertheless, the provision of the member 862 and of the space 863 forfluid flowing toward the passages 825 renders it possible to constructthe lockup clutch in such a way that the number of valves 842 is lessthan the number of passages 825.

[0152] The just-discussed feature of the torque converter and lockupclutch embodying the structure of FIG. 11 can be relied upon inconnection with the construction of the torque converter 3 and lockupclutch 15 shown in FIG. 1. Thus, a fluid flow regulating valve (such asthe valve 542 or 642 of 742 or 842) can be installed on the piston 17 tosupply fluid coolant to the illustrated inlet 26 a. Such inlet cansupply fluid coolant to all of the passages 25 in the friction lining22.

[0153] It is desirable to construct and install the valve or valves 542,642, 742 or 842 in such a way that the influence of centrifugal forceson the regulating action of the valves is minimal, negligible or nil.This can be readily achieved by utilizing relatively small andlightweight plungers in the bodies of the valves. The inertia of alightweight plunger, especially a small or very small plunger, issufficiently small to ensure that the position of the plunger in itscylindrical chamber is not influenced, or is not unduly influenced, bythe centrifugal force which develops when the housing of the torqueconverter is in actual use. An additional undertaking involves suchpositioning of the axis of the plunger in the valve 542, 642, 742 or 842that it is substantially parallel to the axis of the housing of thetorque converter. This, too, reduces the likelihood that the axialposition of the plunger would change in response to the varyingmagnitude of centrifugal forces when the housing of the torque converteris rotated by a combustion engine or another prime mover. Thelightweight plunger can be made of a suitable metallic material (such asaluminum) or of a suitable plastic material. The placing of the valve orvalves as close to the axis of the housing as possible also contributesto a reduction of the influence of centrifugal forces upon the plunger.This can be seen in FIG. 11 wherein the valve 842 is installed radiallyinwardly of the friction lining 825 on the piston 817.

[0154] The valve or valves of the type described with reference to FIGS.8a, 9, 9 a and 10 render it possible to regulate the rate of fluid flowbetween the first and second compartments in such a way that the rate offluid flow is not proportional to the square root of the differencebetween the pressures of fluid coolant in the first and secondcompartments.

[0155] Hydrokinetic torque converters of the type disclosed in U.S. Pat.No. 4,969,543 to Macdonald exhibit the drawback that the rate of fluidflow between the two compartments in the engaged condition of the lockupclutch is overly dependent upon the RPM of the housing of the torqueconverter. Thus, the rate of fluid flow is reduced considerably inresponse to increasing RPM of the housing. This is attributable to heaforediscussed dynamic or kinetic influences upon the conveyed fluid.Any undesirable and/or uncontrollable influences upon the rate of fluidflow are highly undesirable because they could alter the axial positionof the piston (and hence the maximum value of the torque transmittableby the lockup clutch) at a most inopportune time or stage of operationof the torque converter. It has been found that the influence of changesof the RPM of the housing upon the lockup clutch which embodies thepresent invention is negligible, and this is attributed to theaforediscussed feature that the fluid leaving the passages between thefriction surfaces of the lockup clutch is caused to flow at leastsubstantially radially inwardly on its way into the first compartment.It is now possible to ensure that, at a given system pressure in thetorque converter, the rate of fluid flow is low when the RPM of thehousing of the torque converter is low; this renders it possible toemploy a smaller and simpler pump.

[0156]FIG. 12 shows a portion of a ring-shaped or washer-like frictionlining 922 having a friction surface which is provided with meandering(e.g., zig-zag shaped or sinusoidal or snake-like) passages 935. Intheir entirety, the passages 935 extend in the circumferential directionof the friction lining 922. The configuration of the passages 935 issomewhat similar to that of the passages 435 in the friction liningsshown in FIGS. 6, 7 and 8. The width of the passages 935 is at leastsubstantially constant from the inlet to the outlet of each passage.Furthermore the cross-sectional outlines of the passages 935 arepreferably constant or at least substantially constant from end to end.

[0157] A difference between the passages 935 in the friction lining 922of FIG. 12 and the passages 435 of the friction lining 422 is that eachpassage 922 is open at the radially outer portion 922 a as well as atthe radially inner portion 922 b of the friction lining 922.

[0158] The passages 935 can be impressed into or otherwise formed in thefriction surface of the friction lining 922 during the making of thefriction lining, e.g., during the punching or stamping out of a largerblank. In other words, the passages 935 can be provided in the frictionlining 922 before the latter is bonded to a piston or to another part ofthe improved lockup clutch. However, it is equally possible to impressor to otherwise form the passages 935 during or subsequent to attachmentof the friction lining 922 to the piston or to another component ormember of the lockup clutch. Irrespective of whether the passages 935are formed prior to, during or subsequent to attachment of the frictionlining 922 to its carrier or support, such passages can be formed bysimply displacing some material at the friction surface of the frictionlining and/or by removing material from selected portions of thefriction surface. The same applies for all other types of frictionlinings which are or which should be utilized in the improved lockupclutch.

[0159] It has been found that the rate of fluid flow in the passages 935of the friction lining 922 is particularly satisfactory if each turn 946or the single turn of a passage is flanked by two substantially ornearly straight elongated portions or legs making an angle 945 ofbetween 30° and 120°, preferably between 45° and 70°. The angle 945which is shown in FIG. 12 equals or approximates 45°. Furthermore, eachpassage 935 extending between the radially outer portion 939 and theradially inner portion 940 of the friction lining 922 is preferablyconfigurated and/or oriented and/or dimensioned in such a way that aturbulent flow of liquid coolant develops at the inlet and/or at theoutlet (preferably at the inlet as well as at the outlet) of eachpassage. It is advisable to select the shape, the orientation and thedimensions of each passage 935 (or at least a certain number of passages935) in such a way that a turbulent fluid flow is established all theway from the inlet to the outlet of the respective passage. Thisenhances the transfer of heat between such passage or passages and theadjacent components of the lockup clutch when the torque converteremploying the lockup clutch is in use. For example, a turbulent flow offluid in the passages 935 can be established and maintained as a resultof appropriate shaping of the turns 946 of the respective passages.

[0160] The feature that the passages 935 are rather close to each otherand that each such passage extends all the way or at least substantiallyall the way between the radially outer portion 939 and the radiallyinner portion 940 of the friction lining also contributes to moresatisfactory removal of heat from the friction lining as well as fromthe adjacent components of the lockup clutch. The combined length of allpassages 935 in the friction lining 922 can be selected with a view toensure a relatively high or a relatively low rate of withdrawal of heatfrom the neighboring components of the lockup clutch.

[0161] In order to achieve a desirable and predictable turbulence of thefluid coolant in the passages 935, it is necessary or advisable to takeinto consideration the pressure differential between the inlets (at theouter portion 939) and the outlets (at the inner portion 940) of thepassages. In a lockup clutch, such pressure differential corresponds tothat of the pressure differential between the bodies of fluid coolant inthe first and second compartments of the housing forming part of therespective torque converter, e.g., between the compartments 18 and 20 ofthe chamber 14 in the housing 2 of the torque converter 3 shown in FIG.1.

[0162] The withdrawal of heat from the friction lining 922 as well asfrom the adjoining components of the lockup clutch employing suchfriction lining can be further enhanced by providing the radially outerportion 939 and/or the radially inner portion 940 of the friction liningof FIG. 12 with pockets 947 and 948 which can be obtained by depressingthe corresponding portions of the friction surface and/or by removingmaterial from such portions of the friction surface. As a rule, thepockets 947, 948 will be formed at the time of making the frictionlining 922 or at the time of making the passages 935, and preferably byresorting to the same procedure as that which is being resorted to forthe making of the passages 935.

[0163] The pockets 947 and 948 which are shown in FIG. 12 are triangularnotches in the respective marginal portions of the friction lining 922.The illustrated pockets can be used jointly with or replaced bysickle-shaped, semicircular and/or otherwise configurated pockets. Stillfurther, and as indicated by two radii 949 of curvature of the frictionlining 922, the inner pockets 948 need not be aligned with the outerpockets 947. FIG. 12 shows that the pockets 947 alternate with thepockets 948, as seen in the circumferential direction of the frictionlining 922. Of course, it is also possible to shape the friction surfaceof the friction lining in such a way that at least some of the pockets947 are in radial alignment with at least some of the pockets 948, thatindividual pockets 947 alternate with pairs or larger groups of pockets948 (as seen in the circumferential direction of the friction lining922), to provide pockets only in the radially outer portion 939 or toprovide pockets only in the radially inner portion 940.

[0164]FIG. 12 also shows that the illustrated inner pockets 948alternate with the radially inner turns 946 and that the radially outerpockets 947 alternate with radially outer turns of the passages 935.When the friction lining 922 is rotated by a piston or another componentof the lockup clutch, the pockets 947 and 948 contain bodies ofturbulent fluid or at least some of these pockets are filled withturbulent fluid. This, too, enhances the withdrawal of heat by the fluidcoolant.

[0165] Still further, FIG. 12 shows that at least the majority of thepockets 947 and 948 are in at least partial radial alignment with theadjoining passages 935. The provision of the passages 935 and pockets947 and 948 in the friction surface 950 of the friction lining 922causes the remaining, intact portion of the friction surface 950 toassume a substantially zig-zag shaped or a similar meandering,sinusoidal or snake-like configuration.

[0166] The depth of passages 935 in the friction surface 950 of thefriction lining 922 or in the friction surface of a friction lining ofthe type shown in FIGS. 6 to 8 can match or at least approximate thethickness of the respective friction lining. For example, the depth ofpassages 435 or 935 can be such that they extend from the frictionsurface all the way to the other surface of the respective frictionlining. This can be readily achieved if the passages are formedsubsequent to bonding of the friction linings to the correspondingcomponents of a lockup clutch. Furthermore, the passages 435 in thefriction lining 422 of FIG. 6 can be readily provided in the frictionsurface prior to bonding of the friction lining to a piston or toanother part of a lockup clutch because these passages do not extend allthe way to the radially inner portion 422 b or to the radially outerportion 422 a of the friction lining 422. In other words, the passages435 do not divide the respective friction lining into a plurality ofshort arcuate sections. For example, the passages can be punched outfrom the blank of the respective friction lining. The same holds truefor the pockets 947 and 948 of the friction lining 922.

[0167] The provision of substantially meandering (such as zig-zagshaped) passages is desirable and advantageous for several reasons, forexample, because the path or paths for the flow of liquid coolant in thefriction surface of the friction lining are lengthened as well asbecause the fluid is caused to repeatedly flow back and forth betweenthe radially inner and the radially outer portions of the frictionlining. It has been found that it is advisable to provide each passage435 or 935 with at least two turns (such as the turns 946 shown in FIG.12) and preferably with four or more turns.

[0168] An advantage of one-piece friction linings (such as 422 and 922)is that they can be readily converted into hollow frustoconical bodieswhich can be bonded to the frustoconical surface of a piston, housing orother component of the lockup clutch in a simple and time-saving manner.On the other hand, a friction lining which is assembled of two or morearcuate sections (such as the friction lining sections 438 shown in FIG.7) exhibits the advantage that the sections can be punched out orotherwise separated from a large sheet-like blank of friction liningmaterial with a minimum of waste. As already mentioned above, one sideof the blank which is to be converted into friction linings 422 or 922,or into friction lining sections 438, can be provided with a film ofadhesive-coated material; this facilitates the manipulation of thefriction linings prior and during bonding to the pistons or othercomponents of lockup clutches. The provision of such films isparticularly advantageous if the passages are of the type shown in FIG.12, i.e., when the making of passages 935 involves the breaking up of asubstantially circular blank into a number of arcuate portions each ofwhich is provided with a passage 935 and a number of pockets 947 and948.

[0169] Friction linings 422 of the type shown in FIG. 6 are preferred inmany instances because the making of passages 435 does not involve orentail a subdivision of an arcuate blank into a set of discrete arcuateportions or sections. This is particularly advantageous in connectionwith bonding of such a friction lining to a piston or the like. Thus, aone-piece friction lining is more likely to be bonded to a component ofa lockup clutch in such a way that its passages and pockets (if any) aredistributed and oriented in a manner to ensure highly satisfactory flowof fluid coolant along the friction surfaces of the lockup clutch.

[0170] It is further within the purview of the invention to providesuitably distributed passages (e.g., of the type shown in FIGS. 6 to 8or in FIG. 12) in a component other than the friction lining of a lockupclutch. For example, such passages can be machined into the frictionsurface 21 of the wall 9 shown in FIG. 1, and the passages in thefriction surface 21 can be provided in addition to or in lieu of thepassages 25 in the friction lining 22 on the piston 17. If the wall 9 isprovided with a set of suitably distributed passages, they are or can bemachined in the friction surface 21 by removing material from thehousing section 4 in a suitable machine tool or in any other knownmanner.

[0171] In accordance with one presently preferred embodiment of theinvention, the ratio of the thickness of a friction lining (such as 22)to the depth of the passages (such as 25) therein can be in the range ofbetween 1.3 and 2.7. As used therein, the term depth is intended todenote the average depth of a passage in the friction lining. The actualdepth of a passage (such as 25, 435 or 935) can be in the range ofbetween 0.2 mm and 0.8 mm, preferably between 0.3 mm and 0.6 mm. As arule, or at least in many instances, the depth of a passage will beconstant from end to end, for example, because the flow of fluid thereinis more predictable and also for convenience of mass production offriction linings. However, it can happen that, in certain hydrokinetictorque converters, the piston or another component of the lockup clutchwill be configurated in such a way that its width and/or depth varies inor counter to the duration of fluid flow therein.

[0172] The resort to zig-zag shaped or similar passages in the frictionsurface of a friction lining or in the friction surface of anothercomponent of the improved lockup clutch automatically entails at leastsome throttling of the fluid flow from the inlet toward the outlet ofsuch passage. Referring again to FIGS. 6 to 8 and 12, the length of eachstraight portion of a passage 435 or 935 can be in the range of between10 mm and 40 mm, and the width of such passages can be between 3 mm and10 mm.

[0173] In order to ensure that the rate of fluid flow in the passages ofa friction lining or in the friction surface other than that of afriction lining will at most equal or approximate ten liters per minute(such rate has been found to be quite satisfactory for adequate coolingof selected parts of a lockup clutch which is constructed and operatedin accordance with the present invention), and assuming that the fluidpressure at that side of the piston which faces the turbine of thetorque converter is to be in the range of 5 bar, the depth of thepassages (such as 435) can equal or approximate 3 mm. The overall numberof zig-zag shaped or similar passages in a friction lining or in a partother than a friction lining of the improved lockup clutch is preferablynot less than four and need not exceed twelve. It is preferred to ensureat least substantially uniform distribution of passages in the entirefriction surface, be it that of a friction lining or of anothercomponent of the lockup clutch. The spacing between two neighboringturns (such as 946 in the friction lining 922 of FIG. 12) at theradially outer portion (922 a) and/or at the radially inner portion (922b) of the friction surface in relation to the width of that portion of afriction surface (950) which is provided with passages can be in therange of between 0.6 and 1.3, preferably between 0.8 and 1.1.

[0174] The depth of the pockets 947 and/or 948 can match or at leastapproximate the depth of the respective passages (935 in FIG. 12).However, it is equally possible, and often preferred, to provide afriction lining with pockets which extend all-the way between the twosides of the friction lining, even if the depth of the passages is lessthan the thickness of the friction lining because the making of suchpockets is simpler than the making of pockets extending from thefriction surface toward but short of the other surface of the frictionlining.

[0175] The ratio of that area of the friction surface of a frictionlining which remains intact upon completion of the making of passages tothe remaining area of the friction lining is preferably between about0.7 and 1.8, most preferably between 1 and 1.5. Thus, and referring tothe friction lining 922 of FIG. 12, the ratio of that portion of thefriction surface 950 which has been removed to form the passages 935(with or without the portion which has been removed to form the pockets947 and 948) to the area of the remaining part of the friction surface950 is preferably within the aforementioned range. This has been foundto be quite satisfactory to ensure adequate cooling of the frictionlining and of the neighboring parts of the improved lockup clutchwithout overheating of the fluid coolant.

[0176] The improved cooling action of the fluid which can enter thepockets (such as 947 and/or 948) of a friction lining (such as 922) isattributable to the establishment of a so-called drag flow whichdevelops along the radially inner and radially outer portions of arotating friction lining. It has been found that the cooling effect ofpockets in the one and/or the other marginal portion of a rotatingfriction lining is particularly satisfactory if the radially outer inletportion of a pocket trails the radially outer outlet portion of thepocket, as seen in the direction of rotation of the friction lining. Thecooling action upon the friction lining and upon the neighboring partsof the improved lockup clutch can be further enhanced by orienting thepassages in its friction surface in such a way that the fluid coolanttherein flows in the same direction as the aforementioned drag flowsalong the marginal portions when the friction lining is caused to rotateabout the axis of the housing forming part of the hydrokinetic torqueconverter embodying the improved lockup clutch. The drag flow along themarginal portions of a rotating friction lining which is bonded to thepiston of the lockup clutch or to a member (such as the member 24 inFIG. 1) which rotates with the piston is caused by that constituent ofthe lockup clutch which carries the other friction surface. Withreference to the embodiment of FIG. 1, the aforementioned constituent isthe wall 9 of the housing section 4.

[0177] When the two friction surfaces of the lockup clutch are free toslide relative to each other while the lockup clutch transmits torquefrom the housing to the turbine of the torque converter, the RPM of thehousing exceeds the RPM of the friction lining if the latter is providedon the piston or on a member which shares all angular movements of thepiston. Therefore, the friction surface of the housing accelerates thefluid in the passages of the adjacent friction lining. It has been foundthat the accelerating action of the housing (such as the housing 2 inFIG. 1) upon the fluid in the passages of the friction lining (such asthe passages 25 in the friction lining 22 of FIG. 1) is greatly reducedor does not develop at all if the passages are dimensioned, oriented anddistributed in a manner as described with reference to the illustratedembodiments of the present invention. Thus, the influence of the RPM ofthe housing of the torque converter upon the magnitude of torque whichcan be transmitted by the lockup clutch is negligible (especially whencompared to the influence of the housing upon the friction lining of aconventional lockup clutch) or nil. The situation is analogous if thefriction lining is carried by the housing and its friction surfaceconfronts the friction surface of a metallic piston. Still further, thesame advantages or similar advantages can be achieved if the passagesare provided directly in the friction surface (such as 21) of a housing(such as 2) or in the friction surface of a metallic pressure plate(such as the piston 17 without the friction lining 22). This, in turn,renders it possible to employ a friction lining without any passagestherein. For example, if the passages 25 are provided in the housing 2of FIG. 1 instead of in the friction lining 22, such friction lining canbe replaced with a friction lining having an uninterrupted frictionsurface free of passages and/or pockets, or a friction surface providedwith pockets and/or passages whose distribution does not correspond tothat shown in FIG. 6, 7 or 12. Even though some turbulence in the fluidstreams flowing in the passages in a distribution as describedhereinbefore will or can develop due to the establishment of a pressuredifferential between the fluid bodies in the first and secondcompartments when the torque converter is in use, such turbulence can beenhanced (with attendant improvement of the heat withdrawing action ofthe fluid) if the passages in a friction lining or in the frictionsurface of a metallic part (such as the housing 2 or the piston 17 ofthe structure shown in FIG. 1) are dimensioned, oriented and distributedin a manner as described, for example, with reference to FIGS. 6, 7 and12. In other words, it is possible to select the configuration, thedimensions and/or the orientation of the passages for the expresspurpose of ensuring that, in addition to other important advantages, thepassages ensure the development of pronounced turbulence at the inlet,at the outlet or along the full length of each passage or of a certainnumber of passages.

[0178] The provision of one or more valves of the type shown in anddescribed with reference to FIGS. 8a, 9, 9 a, 10 and 11 constitutes anoptional but highly desirable and advantageous feature of the improvedlockup clutch and of the torque converter embodying such lockup clutch.The flow regulating action of each such valve can be influenced by oneor more variable parameters of the fluid coolant, of the lockup clutch,of the torque converter, of the prime mover for the housing of thetorque converter and/or of the unit or units receiving torque from theturbine of the torque converter. For example, the only variableparameter or one of the variable parameters which can influence the rateof fluid flow through one or more valves can constitute the temperatureof the fluid coolant, the RPM of the prime mover, the RPM of the turbine(i.e., the RPM of the rotary input element of a unit, such as atransmission, receiving torque from the torque converter) and/orparticularly the pressure differential between the bodies of fluid inthe first and second compartments. The valve or valves can regulate therate of fluid flow between the two friction surfaces of the lockupclutch in such a way that, when the lockup clutch is engaged, the rateof fluid flow between the two friction surfaces is at leastsubstantially constant within the entire operating range of the torqueconverter. However, and as already discussed hereinbefore, it is alsopossible to select the rate of fluid flow in such a way that it is afunction of the extent of slippage of the two friction surfaces relativeto each other in the engaged condition of the lockup clutch. This istantamount to a regulation of the rate of fluid flow depending upon theamount of additional heat which develops as a result of slippage of thetwo friction surfaces relative to each other. Highly satisfactoryresults can be achieved by employing one or more valves which regulatethe rate of fluid flow depending upon the variations of pressuredifferential between the bodies of fluid coolant in the first and secondcompartments.

[0179] The valve or valves can be installed at the inlets or at theoutlets of the passages or at the inlet(s) of the channel(s) serving toreceive fluid from the passages. Still further, it is possible toinstall the valves in the passages between the inlets and the outlets ofthe respective passages.

[0180] Still further, it is possible to employ solenoid operated valvesin lieu of the valves which are shown in FIGS. 8a, 9, 9 a, 10 and 11.

[0181] The improved hydrokinetic torque converter and its lockup clutchare susceptible of numerous additional modifications without departingfrom the spirit of the present invention. For example, certain featuresof the illustrated and described embodiments of the novel torqueconverter and/or of its lockup clutch can be combined or interchanged.In addition, numerous features of the aforedescribed torque converterand of its lockup clutch are believed to constitute patentableinnovations even if they are embodied in conventional torque convertersand/or lockup clutches. This applies, for example, to the making andconfiguration and utilization of the aforedescribed friction linings andtheir passages, to the utilization of the aforediscussed fluid flowregulating valves or analogous flow regulating means in conjunction withor without the friction linings, and to the construction and mounting ofthe piston and certain other components and/or members of the lockupclutch. Last but not least, it is within the scope of the invention toconstruct and assemble a power train, including a prime mover (such as acombustion engine in a motor vehicle), one or more driven units (e.g., atransmission or a differential in a motor vehicle) and the improvedlockup clutch or bypass clutch in combination with the improved torqueconverter or with a conventional torque converter to arrive at apatentable power train.

[0182] The disclosures of all of the aforementioned US patents, pendingpatent applications and the corresponding US patents and/or patentapplications are incorporated herein by reference.

[0183] Without further analysis, the foregoing will so fully reveal thegist of the present invention that others can, by applying currentknowledge, readily adapt it for various applications without omittingfeatures that, from the standpoint of prior art, fairly constituteessential characteristics of the generic and specific aspects of theabove-outlined contribution to the art and, therefore, such adaptationsshould and are intended to be comprehended within the meaning and rangeof equivalence of the appended claims.

1. A friction clutch for a hydrokinetic torque converter, said clutchhaving at least one pair of annular interfaces that are adapted toengage while rotating in one direction and continuously slippingrelative to each other to effect torque transmission in bypassrelationship to torque transmitted by hydraulic fluid in said converter,one of said interfaces having a prescribed width and at least onecircuitous groove, said groove extending a substantial annular distanceabout said one interface and adapted to direct hydraulic fluid in saidtorque converter from a high pressure cavity at one outer edge of saidone interface and across the width of said one interface in a circuitouspath in at least three traversing passes to a low pressure cavity at aninner edge of said one interface, each of said passes extendingsubstantially the entire width of said one interface, said groove havingan inlet section that defines one of said passes and has inlet that isadapted to open said groove at said outer edge of said one interface tosaid high pressure cavity, and said groove having an outlet section thatdefines another if said passes and has an outlet that is adapted to opensaid groove at said inner edge of said one interface to said lowpressure cavity at an angular location remote from said inlet.
 2. Afriction clutch as defined in claim 1 wherein said inlet section isangled generally opposite to said one direction, and said outlet sectionis angled generally in the direction of said one direction.
 3. Afriction clutch as defined in claim 1 wherein a paper-based frictionmaterial forms said one interface, and said groove is formed in andextends through said friction material.
 4. A friction clutch as definedin claim 1 wherein there are a plurality of said grooves angularlyspaced about said one interface and connected in parallel with eachother between said high and low pressure cavities.
 5. A friction clutchas defined in claim 1 wherein said groove has a rectangular crosssection flow area with a relatively small depth and relatively largewidth.
 6. A friction clutch as defined in claim 1 wherein said groovehas a smooth sinusoidal shape with apexes located closely adjacent theedges that the apexes are nearest to.
 7. A friction clutch as defined inclaim 1 wherein said groove has straight traversing sections and pointedreturn bends joining said straight traversing sections, and said returnbends are located closely adjacent the edges that the return bends arenearest to.
 8. A friction clutch as defined in claim 1 wherein saidgroove has a uniform cross sectional flow area.
 9. A friction clutch asdefined in claim 1 wherein there are four of said grooves equallyangularly spaced about said one interface and there are five of saidpasses.
 10. An annular friction clutch facing for a hydrokinetic torqueconverter bypass clutch, said facing having a prescribed width and atleast one circuitous groove extending a substantial annular distanceabout said facing adapted to direct hydraulic fluid in a hydrokinetictorque converter from a high pressure cavity at one outer edge of saidfacing and across the width of said facing in a circuitous path in atleast three traversing passes to a low pressure cavity at an inner edgeof said facing, each of said passes extending substantially the entirewidth of said facing, said groove having an inlet section that definesone of said passes and has an inlet that is adapted to open said grooveat said outer edge of said facing to said high pressure cavity, and saidgroove having an outlet section that defines another of said passes andhas an outlet that is adapted to open said groove at said inner edge ofsaid facing to said low pressure cavity at an angular location remotefrom said inlet.
 11. A clutch facing as defined in claim 10 wherein saidinlet section is angled generally in the direction of rotation of saidfacing, and said outlet section is angled generally in a directionopposite the direction of rotation of said facing.
 12. A clutch facingas defined in claim 10 wherein said facing is formed of a paper-basedfriction material, and said groove is formed in and extends through saidfriction material.
 13. A clutch facing as defined in claim 10 whereinthere are a plurality of said grooves angularly spaced about said facingand connected in parallel with each other between said high and lowpressure cavities.
 14. A clutch facing as defined in claim 10 whereinsaid groove has a rectangular cross sectional flow area with arelatively small depth and a relatively large width.
 15. A clutch facingas defined in claim 10 wherein said groove has a smooth sinusoidal shapewith apexes located closely adjacent the edges that the apexes arenearest to.
 16. A clutch facing as defined in claim 10 wherein saidgroove has straight traversing sections and pointed return bends joiningsaid straight traversing sections, and said return bends are locatedclosely adjacent the edges that the return bends are nearest to.
 17. Aclutch facing as defined in claim 10 wherein said groove has a uniformcross sectional flow area.
 18. A clutch facing as defined in claim 10wherein there are four of said grooves equally angularly spaced aboutsaid facing and there are five of said passes.
 19. A clutch facing asdefined in claim 10 wherein said groove is an uninterrupted groove. 20.A hydrokinetic torque converter, said hydrokinetic torque converterincluding a lockup clutch, said hydrokinetic torque convertercomprising: a torque input shaft defining a rotational axis; a torqueoutput shaft; a converter housing, said converter housing comprisingmeans for being driven by said torque input shaft; a pump wheel disposedwithin said converter housing and comprising means for being driven bysaid converter housing; a turbine wheel disposed within said converterhousing and in spaced opposition to said pump wheel along saidrotational axis, said turbine wheel comprising means for driving saidtorque output shaft; a piston in spaced opposition to said converterhousing along said rotational axis; at least one friction liningdisposed between said piston and said converter housing; said pistonbeing displaceable along said rotational axis to abut said at least onefriction lining; a first fluid chamber containing a substantiallyviscous fluid, said first fluid chamber being disposed between saidconverter housing and said piston; a second fluid chamber containingsaid substantially viscous fluid, said second fluid chamber beingdisposed within said converter housing and surrounding said pump wheeland said turbine wheel; at least one fluid passage for the flow of saidsubstantially viscous fluid between said first and second fluid chambersthrough said at least one fluid passage, said at least one fluid passageextending adjacent said at least one friction lining; said at least onefluid passage having an inflow portion for the inflow of saidsubstantially viscous fluid thereinto; said at least one fluid passagehaving an outflow portion for the outflow of said substantially viscousfluid therefrom; said at least one fluid passage having longitudinaldirection along its length; said longitudinal direction of said at leastone fluid passage having a corresponding radial component substantiallyaligned along a radius of said rotational axis; and said at least onefluid passage having at least one change of said longitudinal directionbetween said inflow portion and said outflow portion wherein saidcorresponding radial component undergoes a reversal of direction. 21.The hydrokinetic torque converter according to claim 20 wherein said atleast one fluid passage is formed in at least one of said at least onefriction lining, said piston and said converter housing.
 22. Thehydrokinetic torque converter according to claim 21 wherein said atleast one fluid passage comprises a channel formed in the surface ofsaid at least one of said at least one friction lining, said piston andsaid converter housing, said channel having at least one portion that issubstantially nonlinear in a plane adjacent to said at least onefriction lining.
 23. The hydrokinetic torque converter according toclaim 22 wherein said channel includes a substantially radiallyoutwardly disposed inlet and a substantially radially inwardly disposedoutlet.
 24. The hydrokinetic torque converter according to claim 23wherein said at least one fluid passage comprises a plurality ofchannels formed in the surface of said at least one of said frictionlining, said piston and said converter housing, each of said pluralityof channels having a radially outwardly disposed inlet, a radiallyinwardly disposed outlet and at least one portion that is substantiallynonlinear in said plane adjacent to said at least one friction linear.25. The hydrokinetic torque converter according to claim 24 wherein eachof said plurality of channels comprises at least two accurate portions,a first of said at least two accurate portions being disposed radiallyinward and a second of said at least two arcuate portions being disposedradially outward.
 26. The hydrokinetic torque converter according toclaim 25 said hydrokinetic torque converter additionally comprising anexpanded reservoir channel portion provided at each of said at least twoarcuate portions.
 27. The hydrokinetic torque converter according toclaim 26 wherein said plurality of channels are provided on a surface ofsaid at least one friction lining.
 28. The hydrokinetic torque converteraccording to claim 27 wherein said hydrokinetic torque converteradditionally comprises a disc member interposed between said piston andsaid converter housing, said at least one friction lining being providedon a surface of said disc member, said radially outwardly disposed inletbeing provided on a radially outward edge of said disc member, and saidradially inwardly disposed outlet being provided on a radially inwardedge of said disc member.
 29. The hydrokinetic torque converteraccording to claim 28 wherein aid first of said at least two arcuateportions is shaped convexly radially inward and said second of said atleast two arcuate portions is shaped convexly radially outward.
 30. Thehydrokinetic torque converter according to claim 29 wherein each of saidplurality of channels comprises a pair of channels, a first of said pairof channels comprising said radially outwardly disposed inlet, saidconvexly radially inward arcuate portion, and a junction with a secondof said pair of channels, and said second of said pair of channelscomprising said radially inwardly disposed outlet, said convexlyradially outward arcuate portion, and a junction with said first of saidpair of channels.
 31. The hydrokinetic torque converter according toclaim 30 wherein said hydrokinetic torque converter additionallycomprises a disc member interposed between said piston and saidconverter housing, said at least one friction lining being provided on asurface of said disc member, said radially outwardly disposed inletbeing provided on a radially outward edge of said disc member, and saidradially inwardly disposed outlet being provided on a radially inwardedge of said disc member.
 32. The hydrokinetic torque converteraccording to claim 26 wherein each of said plurality of channelscomprises a groove formed in said surface of said at least one frictionlining, said groove beginning at said radially outwardly disposed inletpositioned on a radially outward edge of said at least one frictionlining, said groove terminating at said radially inward edge of said atleast one friction lining, and said groove comprising a multiplicity ofsegments, each of said multiplicity of segments being obliquely orientedwith respect to a radial line projected from said rotational axis, andadjacent pairs of said multiplicity of segments being joined by at leasttwo arcuate portions.
 33. The hydrokinetic torque converter according toclaim 32 wherein each of said plurality of channels comprises four ofsaid segments and three of said arcuate portions disposed between saidinlet and said outlet.
 34. The hydrokinetic torque converter accordingto claim 33 wherein each of said multiplicity of segments issubstantially linear over at least a portion of its length, and whereinsaid hydrokinetic torque converter additionally comprises a disc memberinterposed between said piston and said converter housing, said at leastone friction lining being provided on a surface of said disc member,said radially outwardly disposed inlet being provided on a radiallyoutward edge of said disc member, and said radially inwardly disposedinlet being provided on a radially inward edge of said disc member. 35.The hydrokinetic torque converter according to claim 26 wherein each ofsaid plurality of channels comprises an S-shaped groove beginning atsaid radially outwardly disposed inlet extending radially obliquelyinward to said second radially inward disposed arcuate portion providedwith one of said expanded reservoir portions, thereafter extendingradially obliquely outward to said first radially outward disposedarcuate portion provided with another of said expanded reservoirportions, and thereafter extending radially obliquely inward andterminating at said radially inwardly disposed outlet.
 36. Thehydrokinetic torque converter according to claim 35 wherein saidhydrokinetic torque converter additionally comprises a disc memberinterposed between said piston and said converter housing, said at leastone friction lining being provided on a surface of said disc member,said radially outwardly disposed inlet being provided on a radiallyoutward edge of said disc member, and said radially inwardly disposedoutlet being provided on a radially inward edge of said disc member. 37.The hydrokinetic torque converter according to claim 26 wherein each ofsaid plurality of channels comprises a substantially sinusoidal waveshaped groove formed in an extending circumferentially about said atleast one of said at least one friction lining, said piston and saidconverter housing, a first of said substantially sinusoidal wave shapedgrooves being substantially 180 degrees out of phase with respect to asecond of said sinusoidal wave shaped grooves, with fluid exchangejunctions for the exchange of said substantially viscous fluid beingformed at intersections of said first and second substantiallysinusoidal wave shaped grooves.
 38. The hydrokinetic torque converteraccording to claim 24 wherein each of said plurality of channelscomprising a serpentine groove formed in said at least one of said atleast one friction lining, said piston and said converter housing, sandserpentine groove extending from said radially outwardly disposed inletto said radially inwardly disposed outlet and including a multiplicityof arcuate portions; and wherein said hydrokinetic torque converteradditionally comprises a disc member interposed between said piston andsaid converter housing, said at least one friction lining being providedon a surface of said disc member, said radially outwardly disposed inletbeing provided on a radially outward edge of said disc member, and saidradially inwardly disposed outlet being provided on a radially inwardedge of said disc member.
 39. A hydrokinetic torque converter, saidhydrokinetic torque converter including a lockup clutch, saidhydrokinetic torque converter comprising: a torque input shaft defininga rotational axis; a torque output shaft; a converter housing, saidconverter housing comprising means for being driven by said torque inputshaft; a pump wheel disposed within said converter housing andcomprising means for being driven by said converter housing; a turbinewheel disposed within said converter housing and in spaced opposition tosaid pump wheel along said rotational axis, said turbine wheelcomprising means for driving said torque output shaft; a piston inspaced opposition to said converter housing along said rotational axis;at least one friction lining disposed between said piston and saidconverter housing; said piston being displaceable along said rotationalaxis to abut said at least one friction lining; a first fluid chambercontaining a substantially viscous fluid, said first fluid chamber beingdisposed between said converter housing and said piston; a second fluidchamber containing said substantially viscous fluid, said second fluidchamber being disposed within said converter housing and surroundingsaid pump wheel and said turbine wheel; at least one fluid passage forthe flow of said substantially viscous fluid between said first andsecond fluid chambers, through said at least one fluid passage, said atleast one fluid passage extending adjacent said at least one frictionlining; said at least one fluid passage having an inflow portion for theinflow of said substantially viscous fluid thereinto; said at least onefluid passage having an outflow portion for the outflow of saidsubstantially viscous fluid therefrom; said at least one fluid passagehaving a longitudinal direction along its length; said longitudinaldirection of said at least one fluid passage having a correspondingradial component substantially aligned with along a radius of saidrotational axis; said at least one fluid passage having at least onechange of said longitudinal direction between said inflow portion ofsaid outflow portion wherein said corresponding radial componentundergoes a reversal of direction; said at least one fluid passageadditionally comprising an expanded reservoir portion; and said expandedreservoir portion being disposed substantially adjacent said change ofsaid longitudinal direction of said at least one fluid passage wheresaid corresponding radial component undergoes said reversal ofdirection.